How much is too much when cleaning up a head?

[Volcom]

I'm in the process of cleaning up an 85 22RE head to swap onto my new shortblock for my swap.  The head may need the surface cleaned up, how much can I take off and be OK?  I don't want the timing to get thrown off from me taking too much off of the head.  Any ideas?

[79coyotefrg]

.005  should be fine  .010  if you must,  after that get a adjustable timing gear

[Volcom]

.005  should be fine  .010  if you must,  after that get a adjustable timing gear

Thanks for the reply!