V8-valiant,
I am following your thread closely since I am in just about the same situation as you, as I currently have my 340/420 in the machine shop. Mine will be a street only build and I have both the RPM (non- Airgap version) and a Weiand X-celerator ready for the build. I have not yet decided on which one to run as they are both gasket- matched/painted and ready for a last- minute install.
One thing that I will bring up is that neither one of these intake runners or the carb mount opening’s matched the gaskets that I have for the build. The information on both of these intakes show that they were designed for the 318/340/360 cu inch engine and not a 420. If you haven’t already, you may want to consider at least gasket matching the intake that you plan on using. I had to take a lot of material out of both of these intakes (runners/carb opening) to get them close to the gaskets, while these same gaskets match my heads (ported) exactly.
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