The way I have done it for years is to hold the head upside down in a vice and then rotate (oscillate) the barrel by hand. It works for me.
Yep, that's the way I do it. I took my heads and barrels to Bob Dunn a couple of years ago for some work, and he commented on how well they were lapped (nice to get praise from a professional) so it's got to be "one of" the right ways to do it.
H