So far as the oil seal is concerned, I understood you had identified a slight weep of oil from it at the start of the exercise.
To be sure the valves seal, you need to lap them. This is a simple procedure: you smear their sealing surface with some paste you can get in your local speed shop, put them in their guides to keep them central, and twirl them around for a while. Then you clean both valve and seat of the paste, and look where the paste has abraded them. If you find a continual abraded surface all the way around both valve and valve seat, you are done. After that, you must check the tappet clearance, but you need to have the camshaft and timing cover installed to do that so it is a final adjustment when you are reassembling the engine.
Polishing the ports of your engine is not a normal maintenance operation, it is an engine modification that often increases the output power by a minuscule amount at high engine speed. Sometimes it decreases low speed torque a bit too; rough port surfaces are actually a good thing at low speed.
Have you checked the piston ring gaps?
Have you cleaned the breaker points and adjusted the breaker gap?
