Improvements On A Classic Car

We've all seen the negative nellie how to ruin a classic muscle thread or whatever it is. How about a positive spin?

It doesn't have to be an original "muscle car" per say. Might be just a base model like Vixen, my 64 Valiant. But whatever it is, what are some of the things you would do to make it more of what you like?

For me, put a V8 in it.