Agree with David, the things that were unique to the Sprint are pretty much readily available. Upholstery, qtr panel decals, stripes, etc are available from sources that are finally starting to recognize the market for 71-3 parts. The Sprints also had the Mach1 style front bumper and grill. A missing or damaged front bumper could be a problem, along with any missing blue stripe center caps. If the car is equipped with the "B" package which would have included Magnum 500's, then the center caps are a non issue.
If you have recently bought one or looking at one that needs a home, try to post some pictures of it along with the Vin and door label. We have some Sprint experts here that have forgotten more than I'll ever know about these cars, so feel free to ask about anything you may want to find out about these cars.