Might want to be careful about going to large on the valves, the ports are technically to large to begin with so using to large a valve actually hampers your ability to make torque. You'll lose a lot of pumping power until over 6 if you go even 2mm larger. The intake can benefit, But the exhaust valve is best left stock or just a hair over such as .5 mm. The best engines are built to utilize the power band that you will spend the most time at. Going to large and you shift the power into redline and past. That is typically why 2-1 exhaust are actually a poor choice for an XS. unless you give the pipe adequate room to prevent reversion and the collector and step the header from 1 5/8 to say 1 3/4 then a smoothed and dynamic collector at perhaps 2 then 2.5 a 2-1 setup pushes max power to around 8500. I can keep motors right against redline but pushing 7500-8000 frequently will create some incredible crankcase pressures even with a heiden designed PCV valve. Also clutch life and ring life is drastically reduced and that is if you can manage to keep the intake valves from nearly melting. XSJohn (RIP) had oil sprayers he plumbed into his intake valve covers just to satisfy his tappet adjusters thirst for oil. Hence my pursuit for a roller rocker and perhaps even a more refined oiling system for the rockerbox area. I am going to see if ford roller rockers for i believe it is the Cleveland motors that the rocker is oiled through the rocker body. If so i will try to either adapt or "borrow" the same concept for the xs but include a sprayer at either base, cam and valve base. so even if i stay with an adjustable elephant foot or devise some form of roller bearing there should be adequate oil to push the motor to redline and hold for as long as the motor doesn't literally come apart. the biggest thing afterwards is to have everything weighted the same and dynamically balanced. Think land speed racer type engine. Max horsepower Maximum duration. That way i may not hit 165 but I can keep the heat on the modern day supersport in the corners. They may take me in the straights, but if i can keep the motor at max rpm pretty much 90% of the time they won't get away from me.