Longevity seems to be a strongsuit of the 6BT. My CTDs came with 325k-425k (kilometers) on the odometers that worked. I believe cummins recommends renewing piston rings at 600k? So far no engines have any major issues, and respond well to tuning and performance mods. I estimate I've doubled the power output on my W250's 325k engine (now 370k) for peanuts. My Ramcharger project's engine is getting some gaskets so it wont leak as much oil - and some tuning for more power - no rebuild.
An $8k truck isn't an engine donor. IMO, $4k is about the realistic limit... supposing its a complete running 4wd drivetrain donor... Pull off a job like this guy did...
https://www.dieselbombers.com/diesel-engine-conversions/42163-1992-f250-4x4-cummins-conversion.html
I looked at MDT donors for many years.... same with schoolbuses. Lots of miles, high prices, big ugly hulk to get rid of, and you're trying to adapt and customize the jewelry to work in a much smaller truck. The dodge CTD is already pre-packaged right. Has a trans attached. And if you score a runner, you have an extra truck to use until you finally take it apart. Added bonus... avoiding intercoolers, p-pumps, and NV4500s saves a bunch of '5.9 tax'... and every bit as good, IMO.