VERY well done, Dave!
My bet is that it's a 76. You're about to experience a few unexpected delights, like no more bridge "wiggle," wider/flatter/faster frets, a swept back neck angle, much shorter heel/neck joint for more comfortable playing in the upper register. On this particular guitar, I'm most impressed with what at first glance looks like the original case. Of all my 77s, only one has the original hard shell case with the body molding and the right amount of extra padding behind the neck joint and the horns.