"Could it be that this was a late run truck that didn't hit a show room till early 56 and still had the "y" code body, but still had several of the 55 parts along with some of the new stuff for the 56 models."
Yes (see below). And the Kudu Stabilizer appears to be a part that GMC made standard in 1956 because of a suspension problem experienced in 1955. Perhaps those stabilizers were an option/add-on in late 1955 (6v used as standard in Blue Chip trucks through 1955)?
"I did a bit of research here, from what I can tell (I'm not real well versed in GMC) it's a '55 2nd built at Pontiac. Not sure why it would be registered as a '56, unless it originally cam from a state that registered vehicles by year sold, rather than actual model year. If that's the case, it might have been a late production or leftover '55 stock sold early '56."
"So, GMC made that 101PY Blue Chip Truck in 1955 (perhaps it was sold/titled/first-registered in 1956)"
"As posted above, a late 1955 engine might have been used in truck manufactured in 1955 but first registered/title on 1956."
"Hearing of adjacent year items on beginning/end of year runs isn't a surprise.
...and like Tim mentioned, built in year A but sold/titled in year B, etc."
"GMC would have called it a 1955 GMC Blue Chip Truck.
Call it anything you like. Technically/Apparently, it was a Y-code GMC Blue Chip Truck first registered in 1956."
I sent you a PM.
"I was born in 56 which is one of the reasons I've held on to this beast as long as I have . . . " Look at it this way - your truck did not get its birth certificate until 1956.
