While you mentioned you're focused on the 6V92, most RV chassis were built with the Cummins family of engines, primarily the 5.9 (AKA ISB), or the 8.3 ISC. The Cat wasn't as popular and the larger Detroit diesels were only used in the top of the line coaches. Almost all of those engines were mated to the 3000 series Allison, either the 5 or 6 speed. Just about everyone that owns or has owned a Cummins/Allison combination has been very satisfied. Ditto with the Cat family of engines, although some complain about the smoke at startup.
I have a Spartan chassis under my 1993 HR Navigator, and I'm totally happy with it. I understand the Gillig is also a fine chassis, but I don't have any personal knowledge or know anyone personally that has a coach built on a Gillig.
Only the top of the line coaches from the various manufacturers will have the better chassis and engine combinations. Good luck on your search.
