I will ask Geisler, but you might want to check with Marlo (503) 678-2678 0r Dennis Hough in Eugene,Or.
His phone number is (541) 344-0095. I built him a new chassis about ten years ago for a old roadster he bought from Doc Jeffries, and at that time it had a pair of (I believe) 8:00 or 8:20x 15's on it.
Also, I don't know if if they survived the crash a few years back, but Seth Hammond ran them on that car around that time.
The Portland Swap Meet is coming up in April and I will keep my eye out for you (the glass one, not the seeing one).........................
Bob