People loved classic muscle cars like our '65 Mustang example, mainly because they were fast. Sure, many of them looked great, but it's quite likely that fewer people would remember them if they were slow. Therefore, one of your most important restoration tasks is to rebuild or replace the car's engine.
First, start by completely dismantling the engine. Fuel pumps, carburetors, cylinder heads and compressors -- everything must go. As you did with the car's exterior, examine each part and see what needs to be repaired and which parts need to be replaced.
The ease with which you can find parts for your car's engine varies from model to model. For instance, you can find parts for your Mustang just about anywhere, but if you decide to restore something a little more unusual, like an older European or Japanese car, finding the parts you need might require a little more searching.
You can rebuild the car's original engine if you desire authenticity. However, if it's more of a personal project than something you'd sell at an auction, there's nothing wrong with installing an entirely new motor. Why keep that old 289 cubic-inch V-8 in your Mustang when you could upgrade to a 428 cubic-inch Cobra engine? With a so-called crate engine, also available online and from various parts catalogs, you can custom build your dream car with ease.
Restoring a car is a big undertaking. In fact, this article barely scratches the surface of how difficult and involved the entire process really is. It's not something to begin unless you have plenty of time, money, and know-how. But if it's done properly, you can bring a car back from the dead and up to its original factory specs -- or you can build your own custom machine. In any case, why pass up the chance to finally drive your dream car?