You can do a lot with nitrous but the orignal poster siad he didn't want to use nitous. Also, headers, 4bl intake and 4bbl for a \6 is going to be close to a thousand bucks not to mention the $400 or so for a basic nitrous set up. That is close to the cost of a sb swap.
Building a \6 to make v8 levels of power is something you have to want to do, its not going to be cost effective compared to an engine swap. I will try and dig the photos out tonight and post them. I know a guy that built a multi-point fuel injected and turbo charged \6 for a 39 Willys pick-up he built for his shop truck. Even that engine doesn't have the power of a mildly warmed over sb but for a shop truck its perfect. This guy also has a blown hemi in a 41 Willys pick-up that he uses to scare women and make small children cry.
Can't argue with any of those points, but still, more people will be around the hood of a slant powered hot rod than any other at a car show...simply because they are something different.