[Retro]

Scott you can ask them what they would roughly charge to do it just to get an idea, donors are not hard to find. Either a salvage rig or a bus. If you opt for the 8.3 and a 3060 allison the best years are 93 to 98 with the mechanical fuel pump. 6cta8.3 cummins. The newer 24 valve engines with the capps electronic fuel pump had issues and would be more expensive to install.
If the labour sounds like it will be too much where you are I know a guy in Missouri that will do it reasonably and he is very reputable.