318 vs. Slant value

The only slant cars with any "extra" value is a perfect "survivor", and even then it needs the right buyer. I see little difference in value between a slant duster and a 318 duster, same condition.
You are making a "tribute" car, I say go with the best body, and add all the parts to make it like you want. Like Mopar-Mitch just said.