Martin, where have you been? Missed you. Should be a "fairly" easy swap as Fred indicates. I don't know if 230 motor has side mounts or front. If front, you have to switch to side mounts. Anyway You can use a universal tubular trans crossmember. No welding required.
Fred did not say how to handle the shift? Cable seems to be easier than linkage. A th350 is the best for your needs. you can do a lokar floor shift, very pricey.
This is the best idea I've seen for DIY. Many have copied it and refined it. Basically welding forks together. Making a tooth "detent" plate and a "dog" tooth. Be sure to incorporate a Neutral Safety Switch (NSS).
I'm sure the internet is full of info on "three on tree to automatic". Keep us updated on your thoughts and decision and questions.
