The thing that I like about the 6.2/6.5 diesel swap is that they work for people with more time than money. They are plentiful and parts are typically cheaper than some of the other diesel options. Power wise they can be quite impressive (contrary to popular belief) I never dyno'ed mine but with a few modifications I will put money on it having at least 210RWH and close to 500ft/lbs.
I am a firm believer that GM NEVER offered a perfect year of 6.2/6.5. I owned one that I swore would never hit 50K but I also had one that finally let a rod loose at 550K! The earlier years had better but more restrictive blocks and mechanical injection and the later had poor blocks with the essential cooling updates. The 6.2's never came from GM with a turbo but some dealers offered a Banks made turbo system as an option. Regardless the 6.5 turbo equipment will bolt right on.
Block. Block strength is an issue with these motors. Typically the 6.2's are all pretty decent, but the golden goose is the 82 "red" block (red in color only offered in 1982) as they were strait from Detroit and had much more iron content than any other block. This is a highly sought after block and they tend to be hard to find. Next up would be the AM General blocks that I believe are still being produced today for the military. 96.5-98 blocks are by far the worst as they had oil cooled pistons and were known for premature cracking.
Heads. The 6.5's had the best heads as they flowed a lot more than the 6.2. If may be hard to find a set that aren't cracked (any operating temp over 215* has been know to crack the heads) but it is a worthwhile upgrade.
Cooling. These engines are known to cook themselves from the inside out. The 96.5 and later models had a twin t-stat housing and a water pump that flowed twice as much as the previous years. These upgrades are mandatory imo.
Injection. All 6.2's were mechanical as well as the 6.5's up untill 94. In 94 They switched to electronic injection and it can be a nightmare if you don't preform a few modifications. If you go the electronic route I can elaborate a bit more...
Pro's and Cons:
Pro's
Relatively light at 450lbs. That is more than half the weight of a 6BT Cummins.
Adapts to most GM V8 transmissions.
Very reliable if you pick the right year/model.
Mid 20's for fuel mileage with a light foot.
Powerful enough for any Toyota imo.
Smaller in size compared to other 6+ Liter diesel
Con's.
Overheat easily and will destroy engine without proper cooling mods.
Very unreliable if you pick the wrong year/model.
Glow plugs... I hate them and they are very difficult to reach on this motor. Change them out with the right ones before you install the engine. Cheap ones swell on the ends and make it impossible to get them out of the head.
Poor harmonic ballancer design is known to break cranks. Change this also before installing engine.
Because of the IDI engine design the size of the required radiator is HUGE. It would be tough to fit one in an 80 series. You are going to have to use an aftermarket aluminum unit.
Timing chain also drives the injector pump. This is lame. Once the chain stretches the pump timing is thrown off and they loose power and become a pita to start. There is a gear dive alternative from a company in Canada.
Cold starting. With good glow plugs and a working relay they start okay. These must work for anything colder than 45*. I like the grid heaters that are offered in the Cummins they start very well in comparison.
For the past few years I have been dreaming up ways to put one in my Hilux without butchering it, but so far I just don't see how. This is one of the most hit or miss engines I have ever seen in my life. I loved mine some days and hated it others--seriously. I became so pissed with my 95 that I took it to the nearest dealer and traded it for a Tacoma because I was so tired of dumping money into it. I have been through every known problem aside from the broken crank and it was not a fun experience. In the long run I think you would be better off finding another 4BT and just spending the money. If you are however set on the 6.2/6.5 they can be made very reliable. I know several people with a million miles on a stock engine and one that blew his up at 30K :-\
Try to find one with a serpentine belt for starters the earlier years (aside from the 82) have a lower power output mostly because of the heads.
The dieselpage books are a MUST. Buy them before you even look for a donor engine! These links will help...
www.heathdiesel.com
www.kennedydiesel.com
www.thedieselpage.com
They are no where near the powerhouse engines that the Cummins or Powerstroke are, nor can they handle power upgrades, towing big loads, etc. Fortunately that's not what I'm going for. 
