What motor is in that SS now? 283 I'm guessing? Crate motors are not a bad way to go, but personally, with an SS I would find one to get in it to run and go through the original. I guess it depends on what you want to do with the car, but keeping it original will keep the value higher. Of course you won't hurt it by swapping motors because you can always put the original back in before reselling, but I like those old 283's and 327's, they were good motors too, and underrated in my (not so) humble opinion.