New to the forum

Hi all, just picked up a 75 scamp that runs and drives, pretty solid underneath. Some body rust, needs a full interior and paint. A project for me and my son. First order of business is freshening up the front and rear suspension, a basic tune up and full fluid change as the car runs very well as it sits. Someday plan to swap a 318 or something relatively affordable, along with the trans and most likely the rear end. Any advice or leads on interior parts would be greatly appreciated