just got a 86 GMC burb 6.2 ltr diesel

[kell]

New to diesels, just bought a 1986 GMC Suburban C1500 with the 6.2 liter diesel. Previous owner (two owners ago) changed tranny to a NV4500. I was in a hurry to get a truck and didn't know what to look for, so I think I kind of got a pig in a poke. A friend who is knowledgable about diesels had me take the air filter off just today and look in the intake manifold -- a coating of black oil. Blowby... also, the truck doesn't have an awful lot of pick-up. No way to know the actual mileage, because the speedo, which is original, has a mechanical drive, and the NV4500 has electronic, so the speedo hasn't worked in a long time. Also it's only a 5 digit mileage readout.
I'll do a compression test when I have the chance.
I'm wondering what would it cost to either get the engine rebuilt or swap in a relatively low-miler from a donor truck if I can find one. Also how do you find good diesel mechanics that don't work at a stealership. I've never set foot at a dealership and would prefer not to get started.

[chrisk1500]

If you find a good 6.2 the swap is just as easy as a smallblock gasser....