Ted's Trucks used to be a site vendor on here. IMO you are close enough to go and watch *your* engine 'run' or be tested and pick it up from them. IMO they are way better than the other Scum you listed. Did you know you can still get a "NEW" complete longblock P400 or Optimizer? P400's are going out of production, but, a couple site vendors have both engines while supplies last. (Optimizers are still in production.) FWIW
@Burning oil Leroy Diesel and
@Twisted Steel Performance both carry engines.
Keep the price of a new engine in mind vs. a used engine and work it may need. Your restoration goals may justify a new engine, but, again used engine being "rebuilt" may cost as much as a new longblock.
http://leroydiesel.com/product-category/engine-products/
https://twistedsteelperformance.com/
GM 6.5 engines are simply a bored out 6.2. And this (6.2) is a 1982 step above the olds 5.7 diesel hand grenade. 1982: when emmisions life of an engine was 50,000 miles and 100K was the expected (and warrantied 6.5 diesel engine) lifetime. The sub-par metal used by GM bean counters, high compression stress, combined with overheating of horrible stack airflow and poor reverse rotation water pump design make a perfect storm.
@Will L. can get into the weakening of the thin main webs by the large 4 bolt main design. Don't go over 210 on the temp gauge because the rings WILL loose their temper and blow-by will result. GM castings also are prone to crack (esp. heads) when you get them over 210 ECT. Abuse and maintenance are not factors in cracking other than running hot. The Damper, no not the one for the belt drive the other one, on the front of the crankshaft fails and takes the crankshaft out so inspect it often and replace at 100K.
GM blocks are considered scrap in the professional engine rebuilder world. Yes, a throwaway engine that even the military only does a 0.20 oversize and that's it. The frugal will throw rings at a deglazed cylinder only and machine work cost makes GM cast stuff scrap. The risk of cracking is too high to put that much $ in a GM cast 6.2 6.5 diesel.
Optimizers are improved over the GM cast. Then you have the top of the line 2rd re-design the P400.
Thanks for the input i would rather a stronger block/heads anything better than mine right now it has a bumm bumm bumm nose coming out turbo loses oil psi once warm and knocks and i think its losing tge number 2 ip plunger as its over fueling that cylinder i put new injectors in and even swapped them around if you unhook that injector it stops smokeing