The 6.2 isn't a *bad* engine -- the GM diesels get their bad rap from those oddball Olds 350 diesels -- but it's no Cummins.
As of '82 or so you could get a K5 with the 6.2, so sure, it'll fit into your truck and bolt up. I assume you'd hafta swap motor mounts, but otherwise it should drop in.
I imagine these motors came out of CUCV's or HMMWV's being parted, which means while they have low *miles*, they could have high hours. 'Sokay as these motors, if well-treeated, can go for a long time ... but it's something to be aware of.
The fuel system will be a bit different. You'd have to clean your fuel tank out real well, and the fuel lines have a couple of bleed points and an extra filter or two (IIRC the military ones are a bit different than the civvy, and I only had the military version.) These parts you'd have to source from a junkyard or parts truck or fab your own.
Also, as diesels they don't generate vacuum, so they should have a vacuum pump where the dizzy should be. I don't believe this will generate enough to power a brake booster, so you'd have to convert to hydroboost (the diesels came with this factory, and in any event is a good thing IME.) You'd also have some electrical stuff to do for the glow plugs and would need a controller or relay and switch setup.
You'd also want to make dang sure your cooling system is up to snuff ... the 6.2's came factory with a big honking radiator with tranny and engine oil coolers, so if you have any doubts about your current system, figure on a new (expensive) radiator, hoses, etc.
Gearing also comes into play, as the 6.2 is NOT a powerhouse, even for a diesel. The CUCV Blazers (M1009) had 3.08:1 gears and do okay on the highway ... but they don't accelerate for squat. The other versions came with 4.56:1 and would prolly wheel well, but I suspect they'd top out at maybe 60MPH depending on tire size. (These are all with TH400, mind you, so your truck would be different.) Point being that to get the power/speed you want, you may well end up redlining the poor thing, and their fuel economy at high RPM (never mind reliability) goes into the toilet quickly.
In short, take a step back, and ask yourself why. It's not just a drop in (fuel, vacuum, electrical) so there will be additional cost, and might or might pay off in fuel economy. Here in CA, diesel is MORE than high-test, which further negates any mileage improvement -- dollar per mile is prolly the same.
OTOH, they're rattly loud fun, not bad in a lighter truck like a K5, and butt-simple mechanically... but is that worth the $$?
-- A
. The motor mounts are the same I think. Diesel is around .60 more everywhere I go 
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