"1951 chevy 3100 1/2 ton pickup with 1954 235 engine (installed sometime in the 50s)."

Has it been established that you have a mechanical lifter or hydraulic lifter 1954 engine?
I might have missed that pertinent statement in the posts, above. (I apologize, if this is stated, above.)

What is the engine serial number that is stamped into the block in the ledge to the rear of the distributor?