Hi Fuller, the wheelbase was longer and tire sizes larger than current cruiser bicycle frame setups and varied some between manufacturers. 55" axle to axle length was common & 27.5" x 2.5" or 2.75" tire sizes pretty much the standard. Board track racing bikes on loop frames were 4" frame to ground clearance & 30" saddle height with tank top three or four inches higher. Again these are ball park numbers and individual racers varied. I've stretched two of my bikes to 53" & they ride great compared to the more typical 48" bicycle frame. Straight line stability at higher speeds is much improved, but remember that wheelbase is only one factor in bike stability and won't cover for other frame design flaws. I stick with 26" wheels because of the wide selection of tires available, but if you like the wide and tall look 26" wheels mounted with three inch wide tires stand about 28" tall, but I think they look funny mounted on the front and not a lot of selection of forks to fit these wide and tall tires and a frame stretch would be required on most rear triangles to run them even with 135mm axle drops.
Custom frame & forks is the way to go when trying to match these dimensions. Also keep in mind that the motors were huge when compared to a small single cylinder 2 or 4 cycle engine. The tiny engines mounted in a big frame isn't an authentic or appealing look in my opinion.
Have fun!
Rick C.