Curious if I can run 215/ 70 /15 tires on the 15x7 SS rims) and not hit?

You will have no problems with that size.
http://montecarloss.com/SSThunder/tires.html

They will fit the rims and will clear the rear without problem. However, at almost 27" tall, I'm not sure if they'll rub the top of the front inner fenders of a stock height suspension SS or not - that is unless upflying has run them or knows someone that has (I don't see where the SSThunder link says they fit). I've run 235/60/15s on all four corners with the stock rims, but they're 26.1" which is basically stock height. 205/70/15s would probably clear though.

If you're looking for other than stock sizes, check out this link that gives the typical height and section widths for the different tire sizes based on the rim sizes. Be sure to double check the manufacture's specs before buying, because they can vary a little between brands.
https://tiresize.com/chart/

Thanks all - on that note, in order to push the wheels out a bit more, are wheel spacers recommended?

To do spacers correctly they should be hub centric spacers. Several years ago had a set of hub centric 10mm spacers made for the rear wheels of which I had three different size wheel/tire combos running in the rear and the 10mm spacers was run on all the wheel/tire combos and not have tire rub anywhere
My only regret with those spacers was I didn't have them black anodized.

Last year installed a 17x9 wheel which I could only get in a 12 mm offset. A larger 275/40x17 tire was going on front and rear. The 10 mm spacers where moved to the front wheels to allow proper fit. A 21 mm spacer was then made for the rear wheel fitment and this time had it black anodized. Both the old 10 mm and the new 21 mm spacers are hub centric and do an excellent job of maintaining the hub centric fit.

The easiest place to see, understand, hub centric is look at the front rotors to see the machined area of the rotor that is in contact with the center bore of the wheel.
A spacer moves the wheel outboard and a disconnect of that small in height and lightly tapered area goes away. A hub centric spacer will be machined on both sides to produce the fit to maintain hub centric. It actual has a male and female side. My guess is if a non hub centric spacer is used the max thickness would be much less that 1/4" before hub centric is gone.
1 mm = .0394". 10 mm is a little more than 3/8". Not that thick but necessitates hub centric.


Now with ARP rear wheel studs, Moser axles and the hub centric 21 spacer I have no fear of not being safe and reliable.
Be aware that wheel stud length/lug nut engagement is a huge factor in safety. 100% thread engagement is preferable in my book. In drag racing they wanted to see the studs sticking out of the nuts. Just keep the stud length factor as part of a wheel spacers install.

Everything about this company was first class. The anodizing is done "out sourced" and adds time to the order production and a few more dollars to the cost. Worth the wait.
https://www.motorsport-tech.com/

The thickness of my spacers no where near represent anything close to what is needed with another Monte. My spacers are very unique to only my fitment. For your install I could only hazard a guess for spacer thickness. That wouldn't help you.
I was fortunate enough to have alum "junk" spacers of different thicknesses laying around so I could arrive at that odd 21mm spacer thickness. Two years later and hindsight now says they could have been 22 mm, just a silly one mm larger could have been done. A frame touch up of black semi gloss in the RR tire to frame area could be fixed by another .0394" at that location.
Bob

Bob covered the spacer question. I'll add that hub centric is the way to go. Also, I wouldn't want to run any thicker than 1/4-inch/12mm with the stock studs. Any thicker, you'll need to replace the studs for longer ones.

I'm assuming you found a deal on the "skinny" 215/ 70 /15 tires or you're trying to save a few bucks by going with a 70-series tire? If not, just get the 215/65/15s or go with the 235/60/15s and you won't need spacers to make them look "right" - might be less expensive than buying good spacers also.

I’m putting a set of 86-88 SS wheels on my 83 but for some reason, they don’t look right with the 215-65-15 tires, so thought I’d step it up a height to 70s. I would mind getting it wider, does a 235 clear the suspicion and frame?

I ran 235/60-15s on the stock 15x7", 1985 rims, then I ran 245/60-15s on the rear for a bit of a racked look - plus I needed a wider tire to hook up a little better. The backspacing shouldn't be any different between the years at 3.75" for the 15x7" rims (-6mm offset).

Now, the 1981 15x7" Z28 aluminum rims look just like the aluminum wheels on the 86-88 SS and they have a backspacing of 4.25", or "positive" 6mm (quarter of an inch). What that means is that IF you have the 15x7" Z28 rims, the wheel/tires would move inward 1/2".

It's easily checked with the wheel off by putting a straight edge on the inside wheel lip and measure the depth from the straight edge to the back of the wheel hub mounting pad.

Interesting, I’m look into that tomorrow the measurement

I just measured as you mentioned and I’m at about 4”, so alas that guy ripped me off essentially selling them as Monte Carlo wheels when in fact are 80-81 Camaro rims…. Lesson learned I guess

FWIW, I have 245/60/14 on the rear of mine and have not had clearance issues on the width (but I'm and inch shorter due to rims). I run some 1/8" non-hub-centric spacers on the front and have not had issues, but I'm not using it to the same extent other guys are (just a cruiser). But given the option, do it right, especially going any thicker than what I've got. For me it was hub clearance, the rims were off a '69 with front drums, and they didn't fit on the front disks without a small spacer. I'm definitely using tapered lug nuts to make sure it is as centered as possible, but that was what was available at the time.

If I do decide to use these Camaro rims, can I use a acorn style lug? Ironically, I found a set from my old 91 Camaro RS with the black plastic protectors that screw on.

Hey boys, boy did I pull a blunder. Researching the wheels they are SS wheels not the Camaro. Measure at 3.75. Now a question, they are very bad shape with dried on brake dust, road dirt etc. what’s the easiest ways to get that off short of sanding. I tried a pressure washer and didn’t touch it.