Check out the diesel section on this board. You'd be surprised how much information you can get!
I was looking into dropping a 4D55 into my 86. I hope you found one that you like!
The 4D55 is still in the Astron engine family, so you have a few options. Any wide block transmission will fit. The most common you'll want to look for is a truck that is post 1982 that has a 2.6l (G54b) motor. I personally recommend a first gen (1982-1986) 4wd (AKA Power Ram 50).
Good luck! I'm pretty new to the diesel scene in this truck. I got most of my information from NoahWins, he has several of the diesel engines. Just in-case you want to hit someone up who may know more than me.