You can do a Getrag (stock in a 1st gen), a NV4500, or NV5600. If you want a Getrag, just get a manual trans 1st gen. If you want a 4500 or 5600 I'd probably try to get a newer truck with the trans you want and just swap on a 205 case. No matter which way you go, auto or manual, buy a truck with the trans you want. I think it would be easier and cheaper to swap on the appropriate t-case than to dig up the pieces and parts to swap a trans over. This is all opinion though as I have not personally done a conversion.
Travis. .
Travis. .