Don't know the exact measurements but years ago when I brought the 21A home it fit on my 8'x22' tilt bed truck with the head on it, and two years ago I hauled home a MH 82 with the head on, it fit on my 8'x22' gooseneck trailer.
Did you find a MH 20? if so is it Galvanized? I think I drove by one last weekend at a Mueseum along side the road. Didn't have time to stop and it was cold wet and raining.
I believe the 20 should have had the 201 or 217 Chrysler engine in it, the same engine used in the MH101 so should be 40-47 HP.
After looking closer at this picture it appears to be on a regular car trailer. so maybe they are even smaller than I thought with the narrow tires.
Joe