No sure what the question really is but;
No spool was ever installed from the factory
I believe Auburn was the primary "posi" installed from the factory in a G. May have been some Gov Locks in the early years.
G80 code is original posi was installed.
An 86 SS would have a 7 1/2" rear.
If car now has an open rear, no posi, "one wheel peel" there are options to make it leave two black stripes.
And welding the spider gears to make it behave like a spool is not an option.
The least expensive, logical, DIY, way to get two tires burning rubber is this.https://www.summitracing.com/parts/pwt-92-0775-2605
An average mechanic can install it in a driveway. Having the tools and ambition, new oil and a gasket and done, weather permitting.
Once you say no to a Powertrax the cost of burning two tires off is over double. Now you are doing a basic rebuild on a weak 7 1/2" rear to install the new carrier (posi) which is complete rear dissemble and all bearing/seals and most likely someone to pay to do all the labor. It just gets expensive quickly.
Oh, don't forget the price of burning off tires has gone up a lot. Add that to the cost.