Some new ideas for my Slant

You read wrong. Adding the 2 barrel will make mileage go down. Don't get me wrong, I love a slant. I had myself set to build a long rod motor myself. Had a super nice ported head and all. But I realized that no matter what I did to it, it was still short two cylinders. You will always wish you had done a V8. My advice is after reading more of what you want is to build a nice warmed over 318. Much more power and with the right parts can get just as good and even better mileage than a slant six. Will also be cheaper to build.