If you are having vapor lock issues, you need to look at how you've got your fuel system set up.
You have a '75, so there should be a fuel return line in your system. Are you using it, or did you just disconnect and cap "all that emissions crap"?
Find the fuel return line (1/4") and connect to it by using a mid 70s-80s fuel filter.
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This will allow cool fuel to constantly circulate through the system. If you still have issues, you may need to insulate the line in the engine compartment to keep today's corn fuel from percolating.
Regarding boost for your engine, I wouldn't with that much static CR.
And even with boost, you're still trying to push it through 318 heads/ports- even if you have home ported them.
If you're bound and determined to throw a Paxton on this engine, I would get a set of 340/360 heads (X, J, U, whatever). That will get you the bigger ports to make use of that huffer; and more importantly, those heads have bigger combustion chambers that will drop your CR a point or so. Your call.