Since the '68's are so hard to document (unlike the 7's and 9's, no cowl tag coded info to go by), look at rear end numbers (passenger side axle tube, front side), 10 or 12 bolt, number of leaf springs, auto or std. trans, size and number of gas lines, presence or absence of right side tailpipe mounting bracket in the rear wheel opening. Barring original paperwork or documentation, there is no cut and dried (or exact) way to pinpoint what this car is, or was.
Who knows, maybe it's a Yenko, or a Nickey, or a Dana, or a Baldwin Motion ? That's the fun of it, finding and researching. Maybe it will be one of the really rare ones. In any case, good luck and good hunting. Let us know what you find out, or discover. Most all of us will be glad to try and sort it out.