Need some advice

Most retrofit guys aren't going to use the harness or transmission so they don't really add much in the way of value. You probably don't want to put any more money into it, but you could buy one of the harness and ECU combinations, get the thing running on a stand and sell it as a package ready for someone to drop in.

I also reckon the 6.1 is the go for a retrofit motor, you don't have any of the complications of MDS or VCT of to deal with like the other engines and it has a half decent looking intake on it compared to the plastic jobs used elsewhere.