I had a complete donor truck to start with.
What we did with ours was swap the bell housing over from the diesel to the gasser tranny. If both trucks are the same year it *should* work no problem. The 1985 diesel donor truck had a toyo kogyo 5 speed transmission and the late 1987 gasser had the mitsubishi 5 speed.
Ideally you should use the toyo transmission if you can because it has better and closer gear spread. The 2.3 turbo diesel is peppy, but it has a hard time spreading the gap between gears with the mitsu transmission in our diesel swap. Not a deal breaker, but it can take some more planning to get the most out of it when driving.
The diesel donor was 2wd and our truck was 4wd, so keeping the diesel transmission was not an option. The only snag we had with the bell housing swap was the newer style gasser tansmission had a bolt on slave cylinder and the older one was held in by the bell housing (I think the change over year was 1986). We had to modify the face plate of the newer transmission to accomodate the slave cylinder of the older one. Still working a few years later.
A little late, but hope it helps.