If you are not going to use the vehicle for hauling heavy loads, a 3 speed with a Borg Warner OD will work well with your 4.56 gears. 1955 through about 1966 Chev OD transmissions will bolt to your clutch housing. I think it was 67 when there was a Saginaw OD that is really beefy, but they are scarce. I have been running BW OD behind Y-blocks for 50 years and they work just as well behind a GMC 270 or 302. A 235 doesn't really have the power to to very fast. Especially if you lug it down too much.