I wonder if a Gen I Montero V6 radiator would fit? I've thought about using the spare I have in my Trooper if I ever get it running. The V6 radiator is much much larger than the radiator for my 2.3 yet it looks like it might fit. I would have to do some testing to try it.

There are afordable, quality aftermarket radiators for the V6. Maybe that would be another option for you?

1991 Montero LS 3.0 5-Spd LWB 31" Bridgestone Dueller ATs on stock rims, tan/tan interior/exterior
1986 Isuzu Trooper 2.3 5-spd - partially disassembled, tan interior/dark blue exterior