1981 KZ650 CSR

I recently got this bike for free from my neighbor. It's a project, since it's been on it's side in the dirt for a very long time. Fortunately, the engine turns over after soaking in various chemicals. The rear brake is seized up, so that's unfortunate. All of the controls and other things are in bad condition. 
I've decided to change it by doing a couple of things: changing the rear wheel to a 18" one, and replacing the forks with standard KZ650 ones. I'm sure I'll have a lot more changes coming along, but this bike is pretty bad, but restorable. It's just a fun project. 

Welcome from the UK, the CSR has “leading” forks so the trees are likely to have a different off-set to a regular 650. I would suggest using the trees that are correct for the forks you go with otherwise you are likely to have excessive “trail” which will effect the way the bike steers (not in a good way)

Congrats on the 'new' motorcycle...and it will be a grand learning experience

Welcome.
Sounds like you're going to have a lot of "fun" !
Lots of help here and btw we love pictures.  

By Fun, sf4t7 meant to say, get ready for overcharge on your debit/credit card, ha. 

the seized brake is probably no big deal.  If the brake pedal doesn't move, spray penetrant on the shaft and give it time to work. if the problem is at the wheel and you find a replacement, then the new wheel plus brand new brake shoes would solve that part. if you switch to cast alloy wheels, probably the best match is a 650F or 550A.