1966 Fender Bronco

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and it is possible that that is the original neck, as fender had a bunch of parts kicking around in 66/67/68 from earlier years in the shortscale veriety (can't remember the link to that discussion at the moment)

you might be thinking of the 22.5" scale necks used on swingers, all or most of which have a '66 date stamp though the guitars themselves were made in 1969.
the neck could be original, but likely isn't. the decal is the suspicious part. it's highly unlikely fender would be using up old decal stock so late in the game. especially owing to the fact that fender used up old stock until it was gone before moving on to the new stuff. which is why you see clay dots and spaghetti logos in early '65 but not really any later. they'd pretty much used them all up by then. and if they really needed a decal for a prototype bronco, it's much more likely they would have chopped the model designation off a CBS logo and used that. would've been a lot easier than digging to the bottom of a bin for an old one.

you sir would be correct