maverick,
sorry to hear about a ISUZU DEALER doing that to you, and choosing your fights wisely, yeah, probably too much time passed to really do anything about it, but i would put at least a phone call in.
as far as the engine being interferance or not, i am about 98.634 % that it is a NON INTERFERANCE engine. if i were you, i would go ahead and replace it, and the belt tensioner, and probably the water pump too. merlin got the tensioner, and pump for me and it cost like 220 bucks. which reminds me,
i asked my mechanic for my old pump back, but he didnt have it.......makes me wonder, alot, but ill let it pass....

there are folks on here that have changed the belt themselves, but i think it depends alot on how mechanicly inclined you are. i think the biggest tools you would need on this project it time, and paitence.
good luck with it, i have step by step instructions if you want or need them....actually have about 10-12 pages of timming, etc...and 2 how to's from start to finish.
so keep us posted....

david