This is a real stretch (in memory and time), but I once ground the teeth off the first gear on a 76 Bonneville. It acted like a false nuetral as there was nothing for the clutch to engage to. If memory is sound it engaged & ran, then got to the point of no return and simply stopped. I still have the bit, the teeth are completely gone, rounded off to the same diameter as the steel tube gear mount?? The other gears (2 and up) and clutch was fine.
JH
