I think the seat with a chrome grab rail is a /6 item and that does not fit a /7 let alone an '81 bike. You might buy the grab rail and fit it to a seat that fits your bike? I don't really know about '81 seats. I think there are changes about that period. And with the RS fairing you have a seat with a cowling is appropriate?
Plenty of used center stands around. Buy one. Once you find the center stand that fits you can measure it. There is an after market stand made by Reynolds called the Ride Off stand. Some of us really like those and you can usually find one but they aren't made any more. Maybe you could start a business of building Ride Off stands? We might buy a few.
Welcome to the Asylum. You are now one of the Inmates.
Never memorize something you can look up.