You might be able to get a ‘80 cover over the stock foam or close to it.Oh yeah, the '81 on seat is a ugly as a mud fence. I could never understand why Yamaha (and Honda) discovered 1970s fashion in the 80s.....
It may be getting the bread-knife treatment & a fresh cover.
https://texavina.com/1978-1983-yama...profile-cafe-racer-motorcycle-seat-sku-l4533/
Not appealing to me, but many disagree.