If I don't figure it out, that's probably what I'll do and see what happens. I doubt it's very important though, especially since I'm running an aftermarket stereo anyways. I can't really answer how the other systems work since he isn't very forthcoming on the specific details, however I suspect that's because it's proprietary and he doesn't want someone else copying his design. The best anyone has been able to come up with is that we know he has a custom bulkhead between the PCM itself and the connectors to the factory harness.
The conversion is known to be 100% working with all factory systems on the currently supported platforms (b, f and y bodies), but the d-body had a couple anomalies he didn't know about. The biggest being that it has a CCM, and none of the b-bodies have that. However, the y-body (Corvette's) also have a CCM and he has that version of his kit working completely in unison with the Corvette CCM. All factory functions on the Corvette function exactly as they should. The Corvette and Fleetwood use a different CCM though and handle different functions from one another, so I can't just use that kit. I've provided some info from the FSM on what the Fleetwood CCM handles, and while it is mostly autonomous from the PCM, should anything not function as it should he has assured me he can develop another version of his PCM that will work with it.
Also, the Corvette also had the same (or nearly the same) traction control system (the ASR system) as the Fleetwood, and again it is supposedly functioning just fine with the Corvette version of his kit. I wish I could be more specific, but the information just isn't publicly available as to what he's done to make them work. I do know from talking with him on the phone a few times though, that more often than not the other modules are usually only looking for very basic information, for example vehicle speed. And he can create a circuit in his bulkhead and/or make a tweak to his programming that will transmit the needed info through the correct wiring to the module in the same "format" as it would have been with the original PCM.
I do know from others and Paul himself that it is missing the integration for a couple minor emissions items, specifically the EGR and EVAP systems. He believes he has a way to make them function but has not worked on implementing that. Also it seems to me that someone on the gm-efi forum had a theory on how to get them functional as well, but to my knowledge no one has actually done it yet. Basically swap in LS compatible components (EGR valve, solenoids, etc.) and reactivate them in the tune.
In a few days I should know for sure, but the car should run and function mostly normal, I just need to find out what's missing or not functioning. I won't be surprised if I lose the traction control because I think the CCM sticks its nose into that (but I don't remember for sure), ABS might work since it's not too different from the b-body version, just a difference in number of channels but that should be handled by their respective modules. I'm curious what will happen with the HVAC system. It should function, but I might lose the ability to bring up DTCs and other info from the various modules on its display, won't know until I try. I'm not sure anyone with a Roadmaster has done the kit yet, so although he claims it works with all b-body systems, he may not have tried it on a car equipped with the digital HVAC system of the Roadmaster and Fleetwood.
There's definitely some questions to be answered, but as long as the car is driveable I'll be happy, and I can continue to work with him to iron out the kinks if there are any and get a specific PCM released that I can swap in to make everything work perfectly.