Rattletrap 52-
It sounds like Fred has more experience with this than I do!
I can't tell you much about Mallory v. HEI ignition. I chose to go with HEI 'cause there aren't any points to be adjusting, it puts out a very high voltage spark and because HEI was something that come as a production option on later model chevy 6's so you can pull the HEI set up from the boneyard and modify the distributor a little to work, or you can buy one somebody converted for you and then in the next 20 plus years be able to find replacement/maintenance parts at your local parts house rather then having to buy them from an aftermarket speciality builder. Don't get me wrong, malloy makes great stuff that I've used on other cars, I'm just building this truck for a differnt purpose. So, I guess what you should do is decide what you want in terms of cost, availability and performance.
With regards to the radiator, I'd go with at least the four core one and if you are planning on getting radical with the engine the aluminum one might be worth the money to insure that your investment in the engine is protected from overheating and damaging something important, like bearings, rings, valves, gaskets...
Overboring the engine 90+ is more than what I would do, though people like Tom Langdon have said that it works pretty well. The reason I didn't do it, after considering it long and hard, is that the more modern engine blocks are manufactured to more exacting specifications so you can rely on the cylinder walls uniformity in size. The casting on these older engines was not as precise, so you might get five cylinders that can take an overboring of that amount and one where the cylinder wall would be too thin. So, instead of spending lots of time measuring it, etc... I just went 30 over. I also chose to sleeve one cylinder rather than take it 60 over. If you are really tied to this engine and looking to build it radically or its already so worn that you don't have a choice, the major boring approach might be worth looking into and talking to Langdon and others about. While you are at it, what about stroking the engine?
3/4 or full race cam? A full race cam requires a lot more carburation, head work, etc... I went with 3/4 because I'm not building a car to race, I'm building it to drive every day that has some power and gets decent gas milage. For me a 3/4 cam was a good compromise for those things. Thats also the reason I went with the t-5 overdrive tranny, so that when I'm on the freeway at 75 I'm not redlining the engine. You might have that covered with the highway gears in the rear differential and the 3-spd, though I'm not sure.
As far as dual carbs goes, that's what I'm running. I've recently read some posts here by someone who tried all the different carb combinations on their engine and discovered they all get about the same gas milage and a single 4 bbl on a clifford's intake peforms better and is more reliable. I went with dual carbs for the sexy look, and I'm not ashamed to admit it!
Anyhow... I guess the answer to your questions all come back to the same thing: What are you trying to build, a race car, a weekend cruiser, a show car/restoration or a daily driver? Once you decide that you can figure out how to build the engine.
