if you have an original hydromatic it's not hard to switch to a manual trans, you can put nearly any one behind the 350 and make it work - the original 3spd OD would use the column shift, no floor hole, and the later [68+] 3spd has all syncro, but OD in those years is harder to find .... the T5 would work, the New Process A833 is one I've looked at, 4spd w/ OD 4th ... other possibilities too, don't worry about riggin the shift, someone here will have guidance
Bill
