JeromeSolberg wrote:
Did you check the lifter-valve stem clearance? 0,030 to 0.070 using a special gague, or the gauge can be made by removing the spring from a lifter. Possible that one or more lifters is tight after the valve seats were ground.

The lifters can be tested. Look at the YouTube video from Speedwell garage.

Speedwell Garage testing hydraulic lifters

I have a copy of this tester and could mail it to you for the cost Ross charged me for making it, $220. But it may take a little while for me to get it packaged up and mailed. Or you could contact Ross himself.

These lifter plungers are the same as used on the other 1951-54 engines. New reproduction lifters are available from Kanter and Max Merrit.

New reproduction lifters can be obtained from Kanter and Max. Max also sells the gauge, or it can be obtained from Pacific Northwest Packard club. Note Max sells two different lifter gouges, one they say is for NOS and one for their reproduction lifters.