How much power can you afford? Your wallet will decide how much power you want to get. There is every performance part available for the 350 that you could want. How much of the work are you going to do yourself? My motor is fairly stock and goes pretty good for what it is, but any of the built motors will blow past me on the straights. I have 1.0 over honda pistons, type 1 honda cam, ported head, 2-1 pipe. I am running stock carbs with the choke plates removed and the original velocity stacks from the oem air filters. At Mid-Ohio last year, I was running out of carbs on the top end so I need to go bigger there to take advantage of what motor I have. Start throwing money and time at it and see what you end up with. You might want to pick up a spare motor to have parts to play with.
Vintage racing - old guys on old bikes