I agree with 4spdragtop on this one. Start with some bagging and tagging and get some of those random parts out of the trunk and on a shelf after you clean them up. Then start gathering parts or selling off those that you don't need and gather those parts that are correct for your car. You would be surprised with what you can come up with if you ask around here.
As for as the old buildsheet, it can't hurt to post it to see if a member has that car...a bit of a longshot, but stranger things have happened. I have heard of buildsheets even being up underneath the headliner in addition to all of those other random places mentioned previously. I guess eventually when you get the car broken down enough, there will be a definite answer if it exists or not.
