other than the monocoupe, there's also the rearwin speedster from kangke that you could probably fit a gasser without much issue. but it won't be the 20! something larger would be required.

there's also the dehaviland beaver a cessna 152 and a cessna 185 from KMP that would be fine with the zen 20 (i think since the 23 is fine) comes in two colors.

there's also a Dornier DO27 from vmar.

those are what comes to mind. i have the monocoupe and think it's the best looking classic plane there is!