aramp1
+1y
I'm by no means an expert, so this is just my opinion. I've built several motors, and even worked on a few diesels, but never a Detroit, so everything I'm doing now to my truck, I'm learning for the first time.
Anyway, the 53 series motors will be the easiest. The military used 3-53 in wheeled vehicles and you can find bellhousings to mount up GM transmissions directly with no need to screw with the SAE bellhousing. With each different series of motor (53, 71, and 92) a lot of part will interchange. For instance, a 3-53 bellhousing will fit a 4-53. A 6V92 piston and liner will fit any other 92 series motor and so on. (There are a lot of parts that won't interchange between the inline and the V style motors though, for instance the bellhousings. Anyway, I digress.)
The advantages of the 53 series motors include: they're lightweight (compared to other detroits...the 3-53 weighs around 1000 lbs and a 4-53 weighs over 1200). The six cylinder 6V53 that Campy was thinking about putting in his truck weighs less than a four cylinder 4-71. They're fairly easy to come by. You can get a GM bellhousing for the inline 53s (as previously mentioned). And, they're fairly easy and inexspensive to hot rod. Bigger injectors and add an intercooler and you're making power levels similar to a modern diesel. They came in Natural and Turbo. As mentioned before, all detroits had blowers, but the ones without turbos were called "N"s and the ones with turbos were "T"s. I really wouldn't mess with a non-turbo motor for a swap. It's been done, but I like having a little more power than the next guy. And also, there have been several claims of MPGs in the high 20s/low 30s. (I'm from Missouri, so I'll have to see that for myself).
Check this guy with a 4-53 in his 89 Chevy..