Since you seem to be the Tri-Ang expert did they ever produce HOn3 cars? I found one (suppose to be about 10.5mm gauge) and thought that I could just cut the frame to widen it to accept 16.5mm gauge wheelsets.
That Tri-Ang car was only a couple of dollars so I won't feel too bad if I completely mess things up. I have some Hornby spoked wheels on the way so I'll see what I can make of this TT scale Tri-Ang car.
I've got a couple of projects in mind that I can use those Hornby wheels on. After I get that Tri-Ang TT car in front of me I'll have a better idea of what to make out of it. Maybe a two-seater open-air passenger car, or a shorty caboose?