Being of a certain age (I was at the American Honda Convention when the CB500-4 was introduced to the dealers), I've played with some of that era stuff. One of the things we learned about the old 2-valve engines (keeping in mind that the CB500 was essentially 4 SL125s, sort-of), was valve float as the exhaust side of the head heated up. This showed up when I was running a stroked and bored SL100 in the 125 class on 1/2 mile ovals (I was young and skinny, and....yes....we just rode around wide-open throttle, kind of like Bonneville!).
Anyway, the solution was to dish and polish the exhaust valves (lightening and improving gas flow to reduce the heat in that area). That was a "no cost" project, involving chucking them up in a drill press and using a Dremel tool to slowly dish the valve while it was spinning. Without that step, the exhaust valve would tap the piston before the end of a 16 lap main. At that time we had no options for valve springs...and no money to spend on such stuff. Note that the valve contact condition never happened in a "heat" or an 8 lap "semi".
For cams, we simply had the base circle ground down about .040" and surface hardened. Nothing fancy....just our best guess, which worked out OK. Now you can probably get a WEBCAM cheaper than doing your own.
We often ran Mikuni 28mm carbs, with the slide cutaway hand ground to lean out the part throttle enough to "get by". 28s were easy to come by, as the Yamaha guys were putting on GYT kits and throwing the original carbs away. We also ran the original points ignition with the spark advance welded full up, to prevent the rattling and bouncing at very high RPM. Ditch the flywheel and run constant loss battery.
We had good luck with Powerolls exhaust tuning (which was pretty similar to the pipes you see on old CR77 kitted Super Hawks.) I've made my own megs by gore cutting thin wall tubing, then using lots of hose clamps to close the taper before spot welding between the clamps. You'll find good length info on the internet.
Maybe some pretty cheap fun!