['ol Pinion head]

Dennis that's the earliest 483677 casting 455 HO block casting I've ever recorded. Typically the early Gxx0 cast 455 engine blocks that Ive recorded have been D port application blocks, YG's, YC's

Another note, the '71 WL coded 455HO HD 3spd engines were so rarely installed, even w/o the Fall UAW Strike delaying installs, it is very common to see similar wide date ranges on block casting to actual vehicle build.
Am betting it would make sense for each of the A & F body plants to get a WL coded engine assembly, then for it to sit in the engine bank for multiple months until needed.