I added A/C to my '57 with a stock 235 and a 4 speed. No problems.
I have the stock steering wheel and 19.5" tires. I don't have any problem with the manual steering. I do have a suicide knob on the wheel and find it very helpful, particularly when backing up.
I have the stock seat but felt cramped with my long legs. The seat can easily be raised about 2 1/2" with spacers made from 1/2" iron pipe. Doing this made it much more comfortable for me...no more feeling cramped.
