I bought a 69 RR 383 in 74 engine had been built up but kicked out pushrods, bearing piggy backed. 79 new crank, adjustable rockers manly 509 cam (what had when bought) raced engine 4 years in Duster, fast forward to 92 used cam in 440 for my 64, raced that for 10 years (don’t think I got lifters back in same spot) still in engine today on engine stand ready for the 73 Cuda. Cam had 3 different type spring from single to triples. Still look new. Oh, I paid $250 for RR and still have the 383 short block. What I’m getting at is mainly incompetence in building an engine. IMO