[HawgRyder]

The first problem in lapping the heads to the barrels is to keep the two pieces in correct alignment.
In other words...you must have the barrel (or head) in exactly the correct plane to make sure the grinding action is the same all around the circumference of the seal.
Personally...if i had the heads and barrels machined...i would leave them alone...because the pieces would be smooth and in the correct plane as they come from the machinist.
Bob