Simply put, the 1977 Beetle and the 1957 Beetle are the same car. All Beetle bodies can be altered with body parts from other year model cars. Even SuperBeetle parts (from the doors back) will fit a standard Beetle. Now, it wouldn't be cost effective to try to change everything. However, the floor pans, fenders, hood, aprons, deck lid, dash, etc. will all interchange.

Usually only small modifications have to be made. The major difference, and you can't get around this one, is that the older Beetles have smaller windows. However, the '65 has all the old fenders, lights, etc.; but, has the newer "big" windows. A '68-'77 Beetle with '65 fenders, aprons, decklid, and hood can be made to look like a '65; on the outside at least. I have even seen a late model SuperBeetle with an oval rear window.