I bought the seats from Summit with the covers. I am 6'5" 190 lbs. My back started to hurt but it seemed due to friction (only in one precise spot) and is tender to this day. I bout a thin pad (for sleeping bags) that has thick and thin foam layers, cut to fit, and they've been the best seats since.
I first did the plate of aluminum across the stock sliders install. The first thing I noticed was that my head almost touched the overhead bar! The seats were raised alot (an inch more of seat height and a few due to the upright position). I am now in the process of fab'in legs for the seats that are lighter, lower, and a little farther back. This wasn't a big deal till I installed the full cage. Then my head was way to close to harder objects.
Calmini 5", 32" TSLs, daily driver, work in progress...