I was looking for one thing and found something else. The other day, I was doing a web search and ran across this site that has all of the instruction sheets for the old Roundhouse/MDC "3-in-1 kits" that were produced as well as a limited amount of information on a few that were proposed but never went to market.
A long time ago, I came to the conclusion that I'm more of a modeler than I am an operator; I'd rather kitbash or scratchbuild a kit than I would simply run trains. And... I often find it a lot more fun to build something in ways other than indicated by the instructions. Maybe I'm a rebel without a cause; I don't know.
Anyway, here's the link to the site with all of those instruction sheets. Many of the old MDC cars are still available so if you see something here that you really like, maybe you can whip one up using these directions.
Until next time...