I agree it's a Fastback. My guess is '67 - second letter of the serial # would be a "C". Looks to be original black too, very cool. Not terribly difficult to put that back together.
Here's a pic of a 67 Fastback. It looks like your handlebars, stem and seat just need changed to make it near original. It may have been a rams horn model if it's 67, when they first offered the rams bars. The chain guard would have that logo on it, but yours has been cleaned off. I think that's the only difference from the standard Fastback, which is still a great bike to have.
Thanks to a helpful member on here I got a few parts to help this thing get a little more period correct. Anybody have a front wheel they would part with?