I ran a a CB500 with a CB450 head on it for several years in a sidecar and it made enough to get us around the track and we most always bagged a 1st or a 2nd. I used to get beat frequently by Spinney's CB450, with which at first we were pretty even, but then he started to run away from me. I only learned from a very good source last year that he was in fact running one of Todd's engines in that car, I mean he used to disappear on the straights. I don't mind a little fudging to keep up with everybody else's fudging, but that was gross over-the-top cheating.
However, my point isn't about cheating, we still had fun, but rather that the CB450/500 is a very good engine that will really run well and reliably with just a bit of tweaking. I would simply make a good set of exhausts to begin with, and get rid of those CV carbs in favor of 30-32mm Mikunis, that engine needs more gas/air volume. The only place I ever had an oil leakage issue was when the clutch rod seal blew out once. Take a punch and peen the edges of the aluminum housing around that seal so that it can't come out. That's a 180 crank, so except for blowby, there really aren't crank pressure issues. Still, not a bad idea to drill a breather into the dipstick holder and attach a hose and PCV valve to it and exit it into a catch can. Trim the frame, reweld any seam that looks suspect, spend your money on brakes and suspension to start out with. Tim Courts used to go out on that boat anchor of a 500 BMW and run at the front with it against bikes with much more hp because, simply, he knew how to ride. Big HP is a sad substitute for skill, and listen, to acquire skill is what racing is all about. The trophies come simply as proof that you've gotten better. I used to race a 500 Triumph in the gp500 class, and at the time it consisted of Todd, for one, and some G50's which pretty much dominated the podium. I only won one race, but I did really learn how to ride well through my efforts to catch the front runners, and really that was what I was after. When I kicked up to gp750 on a big Triumph, I had better results because now I was a good match with winning hp.
Have fun, stretch the envelope slowly, ride your own race.