In '54/'55, the PG engines (excl. 'Vette) had the hydraulic lifters, and all other car and truck engines had solids. It seems the 'Vette, even with PG, used solids.
In '54, the regular car engines (excl. 'Vette) had a bakelite/fiber composite timing gear with steel hub. In '54, the PG engine timing gear was changed to an aluminum alloy ring/rubber spacer/cast iron hub (as per the engineering features book**). The 'Vette and truck engines had an aluminum alloy gear. It's not clear to me if the PG and truck gears are the same design. '55 timing gears should have been the same as the '54s.
**The parts manuals make no special distinction between the regular and PG engines as far as the timing gears are concerned. All PASS. are lumped together.
