Leave the original valve sizes in it. You will spend a lot of money for very little performance gain. Bronze valve guides and new valve seats are the lead free gas conversion. Valve stem seals or no valve stem seals is the question. As previously stated, no seals on the exhaust, for lubrication of valve guides. I did my 72 XLCH lead free conversion and put seals on the guided. No problems, rode it from Chicago to California and back. Did the same valve guide update to my current 77 XLH.

 

Ahhh, I see "special cams" interest. The Cam Rule - the bigger the cam (lift, duration) the higher the power band. Translation - weak bottom end. The HOT STREET setup is "P" cams, 10:1 forged pistons, .15 head gasket, S&S Super E, Drag pipes . . . with baffles. Harleys love some back pressure, it helps low end torque.