I called the guy from this place, Hitech. I told him about the carb possibilities and asked him what he thought I should do. He told me something that totally confounded my motorhead comprehension about carbs.
SO I was asking him about a couple carbs I was looking at. He goes: "Just get yourself a standard 4150 750 and bring it in. We've got all we need to make it run E85." I'm all: So I what about the billet metering blocks? You know for E85 compatibility?" He's like: "Dude, don't worry about getting all that stuff. Just get a simple 750 and we are golden." I'm like: "But I'm only running a 300 ci engine. What about low end throttle response?" He returns: "All that stuff about needing to match the max CFM to the ci and redline comes from guys that don't understand how to tune a carb. Guys that are just buying carbs off the shelf and bolting them on. Trust me we can make a 750 work fine on your 300. Then you will have a carb that will work on a bunch of different size engines just in case you change your mind about what you are putting it on." So I'm finally: "… Ok… Huh. Interesting."
I have to admit it flies in the face of all that car mag bs I've read since I first got into cars. Interesting stuff. I ended up getting a standard 4150 650 (4777). Mechanical Secondary, double pumper, no choke. Well I guess that's covered now.