When I was working for Mincom Managed Services in Denver last year I built a Sun Ultra 5 with Solaris 2.8 and had 2 4.3.1 systems on it (can't remember if it was 4.3.1.1 or 4.3.1.2). One was running on Oracle 7 and one was running on Oracle 8. It was a playground for a conversion from Oracle 7 to Oracle 8 that I was mucking around with for one of MMS's clients.
Both systems ran fine. Of course, that was just me testing in it, and it never bore a production load, but they did both run....
As long as you have the MF Cobol compiler for the MIMS code and the Forte C compiler to build the TP (assuming you're running Mincom TP), I don't think it matters....
But as a previous poster mentioned, it wouldn't hurt to call your account manager and get a hold of a previous version of the compatibility matrix (if they still have older versions lying around).
Steve Wales
stephen.wales@riotinto.com