Old Fart, being grumpy comes with old age according to my grand children and they sent me the tee shirt last year. I am waiting to see what I get next week. On cams, as far as I know our 4 strokes "don't come up n the cam" BUT I do know from experiments done on the OS 61 that that engine benefitted from a cam reprofile. We used the cam out of an OS 90 to get different valve overlaps and combined with 55% nitro and a direct feed carby and I think OS 90 valves it went like the clappers.
One of my projects stalled by the move and buggered shoulder was looking at the various cam profiles used in our Saitos to see about interchangeability and what sort of performance increases we could look for. The our motor bike tuning of exhaust pipe trick didn't give much in the way of performance increase on a 50 or a 65, over just leaving the muffler off that I can tell you for sure. Double valve springs, ensuring the valves seat well, I usually do the kero check here (seat the valves in the cylinder, invert the cylinder over a piece of disposable towel and fill the cylinder with kero, if it leaks more "lapping" is required if not you are good to go. As soon as I can get my hands on an old 65 cylinder I am going to look at valve seat inserts. This won't happen until we move into a house of our own probably the other side of Xmas.
Christian traders make exhaust sections (solid and flexible) for most 4 strokes you could look there for a start with experimenting with a tuned exhaust.