['ol Pinion head]

Should not have an M22. The only way that could happen fromthe dactory is if the car was a Pontiac Engineering build & the engineers were testing with a soon to be released '71 455 HO engine. That would be on a Pontiac plant build, so no go down that rabbit hole on an Oshawa build.

'70 455 GTO's when optioned with a 4speed came with M21's. There was some confusion over the years as to why a different coded Muncie was used behind the '70 455 GTO's. That simply came down to different tooth count speedo drive gear on the main shaft for the M21 when installed ahead of 3.31's & 3.55's. That is versus the "6 toother" speedo drive ger used in the original M21's in front of 3.90 & 4.33 '70 performance Pontiac A-body's.

Have prev mentioned on this site, there is a "no groove" 26 spline M21 input shaft that can be confused with a fine spline M22 input shaft. From the dozens of Muncies I've had in here, the M21 input shaft is a later replacement piece from the late '70's-80's. Have had two of these no cut M21 fine spline input shafts; & curently have a '72 M21 in the rack so equipped.