Yeah, you can take a Tempest and badge it like a GTO, put the big V8 and put on the hood, but it won't ever be a real Goat. Another thing is that you can buy a nice original car for 10K and then bust your ass fixing it up, spend another 10-15 K easily and only be able to sell it for 12-14k.
It has to be something that you really, really enjoy doing or you will lose your ass.
My advice is to find a nice restored hotrod that somebody has already dropped 25-30K into and drive it and enjoy it. There isn't anything that will spoil your love for a car more than constantly having to work on it and never getting it finished and just keep dropping more and more money into it.