HVAC unit differences between 91XJ and 88MJ?

I'm in the process of swapping the chassis wiring harness from a 91XJ into an 88 MJ and have a question about the HVAC unit. Will the unit from my 88 MJ plug right into the harness from the 91? Or will I have to swap the entire underdash unit over to the MJ? I'm trying to minimize the amount of crap that I have to swap.

I haven't had a chance to get the MJ apart yet so I can't just look at it. Wondering if anybody has investigated this. TIA.

Brent

Anyone have any experience with this?

The HVAC unit itself is a very small assembly, about the same size as the radio. If there are any differences, I wouldn't suspect there's much difference between the two. Since the dashes are virtually the same in those years, you should be able to swap the HVAC over as needed.

Hmm, I guess I may be confusing things. I was talking more about the unit behind the dash (looks like a big black box) that is bolted to the firewall. It appears to run from just behind the controls to the passenger side A-pillar. I'm more concerned with that part being interchangeable. Sorry for the unclear explanation.

BTT, need a little help.