I think you'll find that the average POR poster doesn't spend a lot of time working on 258's. Most around here tend to favor BIG displacement.
I however am running a Clifford 4BBL intake (very similar to the Offenhauser) with a Weber replacement carb. From what I've seen/heard, Holley is great for street applications, but not so hot offroad. If you are looking to spend the $$$ I would say slap a Weber on it with a fuel pressure regulator.
Had I to do it over, I would probably have opted for a Motorcraft 2100, but that was when I was young and stupid in the ways of the junkyard swap. I have since grown more <IMG SRC="smilies/massey.gif" border="0"> in the ways of the force.