Adding air intake pipe on older 90% Trane for Crawl Space Encapsulation

Hey guys...I'm putting together a scope-of-work for a crawl space encapsulation project at my home. One issue is that I have a 21 year old 90% Trane XE90 furnace model TUC080C942B7 (that runs great) in the crawl space. Since the crawl space is currently vented, all combustion air is sourced from the crawl space. The furnace has a louvered cabinet door and the exhaust is piped outside via PVC through the crawl space wall. There is a sealed knock out in the cabinet near the exhaust where it appears an intake pipe could be connected. However, inside the cabinet it doesn't appear that it is set up to receive a good flow of air via a pipe as the burner housing is in the way. I have photos but can't share them as I'm a newbie.

Does anyone have experience with this furnace and know if it can be modified? I have the original installers manual and there is no info at all on adding an intake pipe. I called Trane but they refuse to give any info or any details and push any questions to dealers. I've asked a few dealers for quotes and either have been ignored or they aren't sure or don't want to mess with it. Replacing the working furnace really isn't an option.

Thanks!

source https://hvac-talk.com/vbb/showthread.php?2226959-Adding-air-intake-pipe-on-older-90-Trane-for-Crawl-Space-Encapsulation&goto=newpost