3 angle jobs are for the seats but the same principle applies. 3 angle seats are better than single but blended seats are superior again. Don't try to waste the stems of the valves, either buy wasted stem valves or leave well alone. They could become weak and snap the head off at higher rpm and if you haven't seen what happens when a valve head comes adrift it usually puts a hole in the piston then gets embedded sideways in the seat. Not good.