Hey Josh, I totally understand you not wanting to ship the monitor around. I was half kidding about renting it out.
You do need the mapping between Fxx values and sensors from the FSM, but they're the same for all Subarus that use the old-style Select monitor as far as I know. I can post them if anyone wants.
I ran into some interesting information recently about the BC/BF Select monitor cartridge part numbers:
1990 498347502
1991 498348400
1990-91 498347601
1992 498348800
1993-94 498349200
1990-94 498347700
So it looks like in 1990 they went through a couple of revisions, and in '91 they released both a cartridge just for the '91 and one for both '90 and '91 (I guess so dealers who already had the 1990 cartridge could just get the 1991-only one). The 1990-and-1991 one had a revision as well. The other few seem to follow the same pattern...
So which one do you have, Josh? Apparently getting 498347700 would be the ultimate, but at least subaruparts.com's database says it might be discontinued. In fact, the only ones not listed as such are the 90-91, 92, and 93-94 cartridges. Maybe Subaru decided allowing a dealer to get just one cartridge for all the cars wasn't a deep enough gouge. Sigh.
As far as still wanting a datalogger, would you consider maybe allowing me to send you a laptop computer, a 1990 ECU, and some custom hardware including a plug that the Select monitor could plug into? I'd try to make the setup power the ECU and have the laptop snoop on what the Select Monitor does when you scan the ECU. I ought to be able to use the resulting data to write a piece of datalogging software so that you could use a laptop (I'd of course want my stuff back

) to log the same data the Select monitor can scan, and make pretty graphs and whatnot.