I have also been through this before. On my 68 Camaro I found that on a 8 1/2" weld wheel with 4 1/2" backspacing the 275/50 looked the best in my opinion. The car was lowered the Wheel house opening was even with the top of the tire. The tire did rub from time to time on the inside wheelhouse when turning into a steep drive at angle. The 275/60 was a little to tall looked too much like a truck tire. I think the 275/60 looks great on a lowered 69 though.
My fronts are 26-7.5-15's mikey thompson sportsmans on a 15x5 ralley wheel (off of a 65 CAPRICE). With derbie caps (I cut the front's down 3/4 of an inch to keep it from sticking out past the wheel) you have to look real hard to see the big-n-little package. Otherwise it looks like 15x8 ralley's from the side.
Yep, you can run a 295/50/15 out back with the right offset (I think 4 1/2) on a 15x8 wheel. If you are running fast through a turn, they will roll slightly and rub the inner fender well slightly. I wouldn't try this on a 69 though, the rear wheelwells don't seem to allow enough room. If a 67 or 68 sits too low (mono leaf springs) you will also have some clearence problems.
and I forgot to reply, no these tires will not stick out past the wheelwell. They are inside from the top lip of the wheelwell approximately 1inch or more. I run these and 235/60 15s on a 15x7 wheel up front with no clearance problems.