Write Jlemond@Bellsouth.net and ask him your questions. I bought a complete heater box for my 93 Rodeo for the same reason. I haven't done it yet. but I understand the dash will come out fairly easy and will be much easier to change out the entire housing than just the core. As for having to remove the A/C, I dunno! He may even be able to supply you with the parts you need for this. He's a great source of new and used parts.
Jerry's a retired Isuzu Factory Training Rep. So he knows how to tell people the best way to do a job.
He suggested once, that I add a radiator sealer in the water as it might solve a small leak like mine.

CJ