Will a 235/60/15 front tire with a 15x8 wheel, 4 1/4 backspacing rub anywhere on the front of a 68 Camaro?

Possibly, but it would be very light depending on the steerring stops in your steering box, but it might rub on the frame rail in a full lock turn.

I have run a 245/60/14, which isnt all that different from a 15" combo and I only experienced slight rub in full lock turns.