My 54 235 had shims in it when we tore it down for a rebuild, and we used shims when we put it back together. Plastigage is used to measure clearance, the shims are used to adjust the clearance. That was in 1976, and we bought shim stock of various thicknesses at the local hardware store. I wouldn't think the 55's would be any different, since they're both the full pressure 235's.
Samantha
