I'm putting my eggs in the OM617 basket, mostly because it was cheap (I bought a whole running car for $900 and probably overpaid). So far so good but I have yet to fire it up in it's new body ('86 S-10). You may want to look at my build thread on here. Besides, when I chose this engine I didn't know any better!

Whatever engine you choose I strongly recommend that you buy one you can hear run and preferably drive down the road. The Benz Diesels are pretty tough but some have been abused/lack maintenance to the point that they are not well. Harbor Freight offers a compression tester with M-B adaptors and while not as useful as a leak-down test it will give you some assurance of the engine's condition. Of course you'll want to check oil pressure, look in the radiator for signs of overheating or bubbles while running (head gasket or cracked block/head) and all the other normal checks. These items are the same as any engine but when buying an engine with a ton of miles as our Diesels often have they're even more important.

While I agree that the 4BT is a tough engine I also agree that they are hard to package in most vehicles. They're just a BIG engine. Not sure how a Scout could eat one - but maybe. They are also relatively low RPM and likely would require a differential gear ratio change or two, assuming that the Scout is 4 WD.

Good luck

Dan