He used III's on The Real Thing, and AFAIK some of the recorded tones on Angel Dust (apparently a lot of the guitar on there isn't actually him) are also III. He switched to using MkIVs live in '93 because of the better switching options.
On a Roadster try EL34s, ch3 with the gain around noon, a little less bass than you'd think, and crank the output master as much as you can. The Roadster will create all the bass you need as you crank up the output and dialing the bass control down a little will tighten it up.