My 235 was on a 4.56 rear end, and I was able to physically drive it at a maximum speed of 74 to 75 mph, but at a dangerously high rpm. I routinely cruised it at 65 mph at around 3200 rpm, but would sometimes increase that to 70.
What really helped me with the additional rpms was upgrading the Rochester 1 bbl carb with a Holley/Webber 2bbl from Langdon's Stovebolt. I gained a lot of top end capability with that swap and it worked really well for my 235.
