Vickery's gunsmithing book from the 30s details how to lap a barrel after reaming it, I can't recall off hand if he did it before or after rifling the bore. Mind you I think he was doing it more as a finishing process to ensure uniformity in the barrel due to the constraints of the manufacturing technology of that era, as opposed to attempting to gain much in accuracy.

From what I have been reading we are basically at the point where manufacturers don't even need to send a reamer down the barrel anymore, sometimes modern gun drilling is accurate enough to go straight to rifling.

Personally I don't buy into the idea of firelapping myself. Too many uncontrolled variables in there for my liking. If I was to lap a bore it would be a lead lap like you describe. As I slowly get myself set up to manufacture barrels (likely several years away with my personal time and budget constraints), that will be something I suspect I will be playing with at some point.