Muscle car restoration offers you two choices: you can restore the car back to original condition, or you can customize the car and turn it into a hot rod. If you customize your muscle car, it may not be worth as much as a vehicle restored to its original condition, but it becomes yours.
Restoring muscle cars to their original condition is the same as restoring classic cars. You'll need to seek out original parts, which can be costly and time consuming. The end goal is a car that's as close as possible to what rolled off the factory assembly line, and that may be worth tens of thousands of dollars to collectors. When it comes to original-condition restorations, you lose value for anything new that you put on, and you gain value for anything original you can find.
Restoring a muscle car to your tastes is a bit different, in that you can change whatever you want on the vehicle. There are many different things you can do to a muscle car if you do not need to keep it in factory condition. While customizations don't command the same resale value as restorations, then can be worth more than the parts and your time, if you put the effort into creating something with a lot of power and a unique style.