I've got an SR500 I've played with for the past nearly 20 years. It has a tail section that is a bolt on and I'm thinking of selling. It also has a nice Manx like high pipe a freind and I built from mandrel bent tubing I got from JC Whitney. I also installed a Honda VF500F right side caliper and a different Honda master cylinder to it. Another mechanic friend and I built (mostly him, because they needed to get the parts out of the way when moving the shop) it up with a Wiseco 528 9:1 piston, mild cam, and a 38 or 36 Mikuni (never measured).
Currently it ran for 5 minutes or so about 6 years ago and was shut down to await wiring. It's now in transition again after I moved.
Take a look at my photos on Bike Pics, shortcut below in my sig. Like I say my seat may be for sale, but I also can tell how simple it was to build. The pipe not so simple, but with a good TIG welder as a friend it can be done as was the brake bracket.
It's always great to read and see about old Yamaha 500s. I love the pure stone axe simplicity of them. Although I have no idea how the self-canceling turn singals ever got there. I mean a single two valve kick start carbureted engine with no counterbalancers or gimicks... how cool is that!
As for starting, I never had any problem after a 500 riding friend (the welder/mechanic) gave me the specifics of doing the drill. I don't bother with the little window thingie. I just kick over until I hit TDC,(can stand on the lever at that point) pull the comp release lever and ease it slightly over TDC, then give a good hard kick. Mine usually fired within a kick or two depending on if it was warm. It was all by feel. It was also a whole lot easier to do on the centerstand, but I could do it standing over the bike too. On the side stand wasn't so easy due to the angle of lean. If it popped and stallled about 6-8 good kicks with the compression release opened would clean it out to start again fairly easily... but kind of a hassle and a bit embarrassing when stalled at a stop sign or signal in traffic..