4X was used on 400 and 455 Pontiac engines. Fortunately, Pontiac engines are not overly sensitive to lower than "normal" compression ratio.
Pontiac production rods are mostly either just OK (cast iron, need ARP bolts) or real pos (forged production rods used in 1959-'62). There were decent factory Pontiac $uper Duty rods, but why even think about them when there's cheap aftermarket forged rods everywhere.
I'll reserve comment on "slapping cars together with left over parts", except to say GM might have lost their balls, but Pontiac didn't. Pontiac stuck to their guns longer than anyone else- they had a 455 Firebird as late as '76 IIRC. Yeah, it had low compression, but the raw material was there at least.