IIRC the 71 318 is still a 9.2 Scr/ hi-test fuel, engine; which is already running close to max pressure for pumpgas.
I would just install any small-port 4bbl intake on her, and the cam pirated out of the 360, installed with an Ica of 54*, and call it done.
Yes, you'll lose a lil economy due to the bigger cam, but it will be so worth it, especially when you find out that you can likely tune it for 87 gas. And that would pretty much get you back to par as to cost per mile.
But I gotta warn you;
If yur running hiway gears like 2.76s and a lo stall convertor under 2000, NONE of that is gonna make much of a difference at WOT, until about 30 mph/3000 rpm.
Yur best bang for money spent is to increase the stall; and
second best is to increase the torque-multiplication of the rear gears.
then the 4bbl
then dual exhaust
then the cam
or
just install the 360.