Thanks for the comments guys, I appreciate it.
Rich, I had the RK GP-9 already and was going to scratch-build new pilots but picked up the Red Caboose kit at the O scale show in Indianapolis. It sits a little high but nothing I can't live with. If I come across an Atlas chassis I'll probably make the switch because I really don't like those RK side frames. I thought I might be able to make Lionel frames work but the truck center-spacing is different (RK 8.5' vs. Lionel 9.0'). And you're right about hard working geeps, I like 'em crusty!
Joe