There is actually a huge difference between the 76 and 79. Not only are the headlights different but the 76 model had actual bumpers. If you look at the pic of the '76 you will see what I mean. The rear bumper is the same as well.
Additionally the interiors were completely different. 79 was the first year for the style interior it has.
My recommendation would be to get an early 70's model for the interior and try and scratch build the bumpers on the body of the 79. Would also need to fill and shave the vents in the fender of the 79 as well.
Otherwise keep an eye on ebay for a 74 - 76 model I think they were made at least.