If you are replacing the original powerglide with a later TH350 you have some work cut out for you. You will need an adapter and starter ringgear (availabbe from Buffalo Enterprises), an open driveshaft rear end, new driveshaft, starter (probably 12 volt due to ne mounting) and rear trans mount.
I'm pretty sure the TH350 will be lighter which is good and has 3 speeds to make the little 235 seem to have more HP. Good luck