Variable it seems...Some say at 80inches...some say 1980...two different deals!
I generally don't trust the Vin# for that kind of information...especially on equipment that is this Old..and known to have been Dealer rebuilt sometimes on the Showroom floor!!!
I always roll the motor over...And Look...Hell once I found an S&S flywheel I didn't know was in there!!!!!

 

you can check it yourself easy - take the timing plug out - lift the rear wheel so you can turn it counterclockwise - take the sparkplugs out - use a small 5 inch screwdriver put it into the Front plug hole and turn the motor over till the screwdriver is at full mast - look in the timing plug hole and see whats in it the vertical line or the dot

vertical line is late shovel wheels 1978 they changed the motor BUT giving to true harley they used up old stock haphazardly so an exact date cant happen

and the dot being TDC is early wheels and favoring the back of the hole it actually TDC not the center