Whatever you do, don't take it to the dealer for brakes unless you're spending someone else's money. There are plenty of places to get brakes done for much less than any Isuzu dealer.

My non-Isuzu front brake pads were slightly large for my calipers. The actual metal part of the pad--the pad 'frame' for lack of a better term--was too large for my caliper. I used a bench grinder to remove half a millimeter or so of material and the pads were still snug in the caliper. If you don't have a bench grinder, a coarse file would probably work. Obviously, you don't want to remove too much material. Too small could be dangerous.

OTOH, you could always take the pads back to the parts store with the caliper in hand and exchange them for some that fit better.