I finally got all of my other projects cleared out of the shop, and was able to start on the ’89 RS – LS1/T56 swap on Saturday. [Not bad, considering I wanted to start this in October] Since I have (or had, rather) a good running and driving donor car, I am removing everything as the factory assembled it. I have removed the engine, trans, engine bay harness, and dash "sub-assembly" without cutting a single wire. The idea is to just plug everything back together when it all goes into the ’89. I’m hoping to be into the re-install on this coming Saturday.

So, now to my question. As I’m pulling everything, I see the HVAC system and wonder if it would be totally unreasonable to try to install the entire box in the ’89. I thought that I read that someone did this, but he wound up using the firewall from the 4th gen. Can the 4th gen box HVAC box be made to fit the 3rd gen firewall, or can the 3rd gen firewall be cut to accept the 4th gen box?

 

Ah... just found this:

https://www.thirdgen.org/forums/inte...dash-more.html

I will probably be shamelessly ripping it off.

 

That is pretty extreme... he did quite a job there.
Ghettocruiser put a complete 4th gen a/c in.... pretty much using a modified 3rd gen HVAC box.
Check it out in "Here we go again". Lots and lots of pages to piece through, but all good stuff. Try a search on the thread.

https://www.thirdgen.org/forums/ltx-...-go-again.html

 

I'm about three hours into this HVAC swap now. I've been trimming off small pieces to try to keep the collateral damage to a minimum.

It looked like vjgillespie just opened up the firewall and everything dropped into place; that has not been the case for me. I had to trim out and reshape some of the upper firewall area in the passenger compartment in order to allow the fresh air intake to fit. Maybe that's where the difference lies?

I'm planning to put a few more hours into it tomorrow (if I can scrounge up another body saw blade). It's really close to fitting properly, but I want to put the dash over it and make sure that the vents are where they need to be before I tack the mounting flange in place.

I'll try to get some pics of the extensive modifications required to pull this off.