The '76 , being a rubber bumper car, is an inch higher than the chrome bumper cars so could probably run the low tires with less problems than I do. The only place mine drags is like I said on speed bumps and also some steep driveways the tail pipe scrapes.
The 185/65 sounds like a good compromise.
Right after I bought the last set, I ran an autocross and won in my class and with the old ones, I didn't even come close. They made a big difference there. The old ones were Sears Sport radials that were quite old and hard and the new ones were Dunlops with much better grip. So that was a factor along with the size difference.