I don't know anything about these guys except that they're local (Tacoma) and advertise a lot of JDM Isuzu engines on Craigslist:http://www.japaneseautoengines.com/
Here's one of their current Craigslist ads: https://seattle.craigslist.org/see/ptd/5874129790.html
The only problem with a used engine is it may have the oil burning problem anyway. Anything older than the 2002 model with screw-in PCV valve (vice push-in valve) isn't supposed to have the improved oil drain holes in the pistons.
You could pull 'er down for a rebuild but these aren't the easiest engines in the world to work on. Has been done, though. You could rebuild with improved pistons. Of course, your 2002 is already supposed to have those! Go figure!
Funny thing is, GM used to say that any piston slap that went away when the engine was up to full operating temperature was OK!
I ran a '95 Swift 1.3 for thousands of miles with piston slap in the morning. When I pulled it apart for a "refresh" all the bores looked perfect, with no scuffing, and cross-hatching still present. Installed new std pistons with Swain Tech anti-friction coating and while this did help a bit, there was still a bit of clatter when cold. Didn't worry about it though, the engine ran great, used no oil, and was going strong with 100,000 miles on it when I sold it to my nephew. Almost 5 years later he's put at least another 25,000 on it and the engine runs like a swiss watch. I don't think the piston slap is going to be a problem!
On yours, hard to say whether the slightly excessive piston skirt-to-cyl clearances are causing any problems, or even oil-burning. You could pull your plugs and see if any of them are noticeably worse than the others. But this engine has a rep for oil-burning, so there you are.
You might consider doing the carbon-cleaning regimen then see how it does. If the oil-burning improves, I'd be less inclined to tear the engine apart if the piston slap is the only problem. Unless/until it doesn't go away when the engine's warmed, then that's a real problem.
And if the oil-burning continues or gets worse after cleaning, then yeah, the only likely solution is to pull the engine for a rebuild. Unless you can find a good-running used engine that you can prove doesn't use oil, it's far less risk to rebuild so you know it's done right.
Anyway, G'luck with the carbon-cleaning, not much to lose at this point by doing so........ed
p.s. Craigslist is your friend, I've seen more than one late-model Troop with a rebuilt engine then the tranny blows! Going Cheap!!!