Tallest tire fitment on rear of Scamp

Hi guys,

Im trying to figure out my RPM, gas mileage issues and some of the suggestions where to run a taller tire. What is the tallest tire that will fit on the rear of a 71 Scamp? Can we squeeze a 28", 29" etc.... in the opening?

I believe 9.25" wide is the widest that will fit, but I would like to find wide and tall.