I just responded this week to a question another Forum member PM'd me on. The issue with the TT2 is the negative offset cause by only 3.75 BS. I believe this member had only 3.50" Back Spacing. This person's car was a 1968 Camaro. Out of respect for their privacy I won't mention who they were but we had a nice conversation over PM's and I did my best to help.
Here is the deal. I wasn't born yet when the first 1968 Camaro's rolled off the assembly line in Sept of 1967. But I do know this. The 1968 Z28's had E60x15 tires. Maybe E70x15. I believe E60x15 to equate to P215/60/R15. The P235/60/R15's will rub with that backspacing. I have a 1969 Camaro w/ 15x7 Rally's and I don't have any issues with rubbing and I run P235/60/R15 all the way around. That is because of the backspacing on Rally's. I also have disc brakes on the front of my car and that could make a difference. Most if not all drum brake cars received 14x6 if they were not Z28's. Some SS's received 15x6 if I recall. Most Rally's were 15x7's.
Remember in 1968 cars were still using Bias ply tires. Bias ply tires have more of a square shoulder where as radials have a more rounded shoulder to improve handling & cornering. But the rounded shoulder also will cause tire rub as it increases the contact patch which is known as the footprint of the tire. Just because a tire is a P235/60/R15 form two different manaufactures does not mean it has the same footprint/contact patch. One could still be taller and the other wider depending on the castings/moldings & design by that manufacturer.
Please note: I was in the tire & auto service indurty from 1989-1998. Mostly as an assitant service manager or service writer. Tires were my specialty even at new car dealerships. But since I left the business in 1998 I no longer consider myself an expert in anything and I humble myself everyday when it comes to learning about old cars or new cars. That way I can still learn new things instead of being some arrogant jerk.
Here are 2 helpful links. http://www.turbinecar.com/tires.htm
Drag your mouse over the photos to see how skinny the tires were on these cars.
In my humble opinion in your case, there are only two ways to avoid rubbing--especailly if it's a 1968.
1) Go to at least a 4.25" Backspacing
2) Install P215/60/R15 tires instead
Generally speaking you can get more tire in the front of a 1969 than you can a 1967 or 1968 but you can get more tire on the back of a 1967 or 1968 than you can a 1969. FWIW In 1970 GM went to a wider front tire for the Z28's & Trans Am's
P.S. Don't just take my word on this subject, ask some others as well and get their opinions.
SSG&H aka Greg