right, On those sixes,due to where the Intake valve is positioned in the combustion chamber you must sink the valve the same amout as the mill job to provide valve/piston clearance during TDC begining of intake stroke. So McGurk's recommendation is to save a little effort and use the Pass head which will give you some compression increase without the need of milling and the sinking of the intake valve. I'm not certain, but it seems that both truck and std shift pass heads have 1-7/8" dia valves, but the Pass PG head uses 1-15/16" dia. intake valve. Its been some 35 years or so since I was messin' with that motor- getting a little fuzzy. That and wether you use Palmolive for dishes or Tide, both are good but Tide is sure rough on your guitar calluses!
