Depends on what "gear head" you ask. I never liked doing a leak test after lapping unless it was on a re-machined head
assembly with new parts
New or old guides? Any stem wobble in the guides?
New or old springs?
Were the springs tested?
A decent valve lap can fail a leak test but still give hundreds of hours of service
Used guides have their own wear patterns that will affect seating angles during static testing.
Weak/older springs can affect a leak test. Always do a spring compression
check. You can do it with simple tools.
I used to do a lot of grinding and lapping. On older engines that I was reusing the old parts
and just trying to squeeze a little more life out of, I always checked the stem to guide, and if they were still fairly tight.... I would lap away. If they had wobble......new guides at least
A valves position to the seat (static) is not what the position will be when the with the engine
running. This goes double
when you are reusing the old parts. The assembly will find it's own operational seating angle after it's been running for a while and seat accordingly.
Take a close look at the any valve assembly after a tear down and you will see how each assembly has a very slight wear angle compared to the other valves.
I prefer bluing the valves when reusing older parts because the seating angle between the seat and valve is the best you can hope for in a static condition anyways.