Make sure when lapping you do just enough to grey the seat and valve sealing surface, don't want to grind them too far into the seat. Lap with back and forth motion do not try to do it with a drill. There are special lapping tools that are basicly a stick with a suction cup on the end that you roll back and forth between your palms like you were trying to start a fire with a stick. Also be sure to match 1 valve with 1 position so the same valve goes back in the same spot it was lapped in.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!