I'm looking at DPR's site and i'm trying to decide if i should go with them or portflow to do my headwork. On their site under services they have some things under the diffrent stages that i dont know what are and would like to find out. Here's the list.

What is/are....
01.Back-Cut Valves
02.Radiused Blend Seats
03.Port Faces Lapped Flat
04.Decks Milled & Lapped (i know what milled means but i'm not sure what lapped is).
05.Radiused Cut Seats


Any Advantages/Disadvantages to any of these?