I did 15-20 cam installs (at least 10 different cams) in the 305HOs (SS, Z-28, T/A) back in the 80s and early 90s. By far the best running with the stock 2000-ish rpm stall was a 205/215-112 Lunati and a custom grind 206/212-110 Comp. The biggest off the shelf cam that I would eventually end up installing was the 212/212-110 Comp 260. The last one I had personal experience with was still a few years ago and was a Comp 4x4 206/214-111 with 1.6:1 rockers in his L69 Z-28 (new springs and a mild pocket port clean up on the heads). My buddy and I were both extremely pleased with the outcome and it didn’t sound much different than stock.
I always did before and after ETs with an accelerometer when I swapped cams, so the cams above really are what I know to be really nice performers in a stock SS with the stock stall speed. Be careful though because if the transmission has been rebuilt it's possible they replaced the HO converter that stalled around 2,000 rpm with one that stalls around 1200-1400 rpm. If that's the case, go with smaller of the cams above. If you go too big with the cam on a low stall speed converter, the car will be sluggish and can actually run slower in the quarter-mile than the stock cam.
You'll definitely need to replace the timing chain with the mileage you have on the car and would recommend changing the valve springs to the Comp 981-16 springs for the cams I listed. From what I can gather, there is a problem now-a-days with the flat-tappet hydraulic lifters. Might want to check out Mike Jones Cams, http://jonescams.com
, I found out recently that he's one of very few places that sells made in USA lifters.