I remember seeing a photo of Sem riding that giant wheel, and it had giant blocks on the pedals to help him reach. And he rides with about the same seat height I would. I think that was the 73", but they first built a 72", and then broke their own record, possibly. Probably because they thought they could manage a slightly higher seat, perhaps! If I remember correctly, the 72" was called Large Marge (yes, before the tire of the same name), and the bigger one was called Intense Hortense.
Looking for a Sem Abrahams link, I came across this one, for Denis Frisoli, the guy who most likely rode the tallest unicycle known to have been ridden out in the open (without any rigging to catch him). In the video it is said to be 30 feet tall. It’s ridiculously tall for something to be ridden freely! He has to circle around the Jumbotron in the Philadelphia NBA stadium, where he performs it in a halftime show.
https://thetowerofdeath.com/
Sem is on Facebook, or can possibly also be contacted through their Cirque Amongus website: https://cirqueamongus.com/
What I know about really big wheels: The 63.5" wheel I rode in 1983, which probably had 5.5" (140mm) cranks, or longer, had me at my leg length limit to reach the pedals. You would have to be pretty tall, which you are, to add another 5" on top of that. But I don’t see any reason why blocks would be considered a problem if you can’t reach. Go for 80"! 
