Roler parts exchange, What parts don't interchange? Options

[restore2seater]

I am coming to the conclusion that the restoration of my 914 might not be worth the expense. The time issue of replacing sheet metal and parts of the frame isn't that big of deal to me since it's my time thats being used. Even though it can get frustrating at times. If it was easy or no challenge it wouldn't be worth doing. Like most 914s from the midwest you really don't know how bad the rust is till the car has been stripped.
Other than the dash and the front trunk area I have stripped the rest of the car. Everytime I peal back another layer of parts I either see rust or PO attempt at hideing the rust with big globs of bondo.
I have split the engine case and it looks to be in good enough shape to rebuild. I havn't taken the trans. apart yet but from what I've researched about the trans. the only major problems that can occur are with the linkage and first gear.
The interior is in decent shape other than the carpet. There is no carpet. All the glass is in good shape also.
I have a 1973 1.7L.
My question is if I could find a decent roler that someone would sell me how much of my 73 will interchange with other cars as far as different years go?