I don't know what your top speed with a 235 could be. With a bone stock GMC 270, SM420 and 3.08 gears I have no trouble running 70+ mph. I don't think I've ever tried to cruise at 80, but I think it would do that.

I don't have an overdrive transmission which would probably increase my speed. Swapping to a bigger six like the Chevy 261 or GMC 270 or 302 is a much easier swap and would give you the speed you are after.

With the original brakes I wouldn't want to run much faster than 55. I've got modern drums on the rear and disk on the front.

1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble...