I've made an adapter plate for swapping motors on a lathe before, but it was in the other direction. The original motor was one of the old style motors with a much larger overall size. I replaced that with a smaller Baldor of the same HP, but had to make an adapter to raise the motor to put the shaft roughly the same place, as well as extend the overall footprint to get to the bolt holes on the machine motor mount.
I think trying to go in the other direction might be a bigger challenge honestly.
It definitely sounds like the original motor has issues if it's bogging down on heavy cuts and doing the weird stuff of running in reverse. I've had two 13" Sheldons with 1hp motors and never recall the motor bogging down on heavy cuts...maybe I was going easy, but I don't think so.
I'll also say that I have seen a huge difference between quality electric motors and cheap imports...regardless of what the specs on them say. For example, I had a Baldor 1/2hp grinder and a cheapie import 1/2hp grinder with similar specs. Using a wire wheel and leaning heavily on the cheapie I could get it to bog down nearly to the point of stopping (not a recommended technique). The Baldor would slow a little, but nowhere near as much...not even close.
I doubt you'd have issues with a quality 1hp motor that's working properly.
