To me, "mildy built" means pump gas and perhaps 425hp.  Holley 850 cfm, List # 4781.

LO

If you are on a dual plane, 850 CFM (the 4781 or 9381).
Single plane, anywhere from 700 (small cam) - 850 (larger cam).

Of course, anything from 650-850 will work no matter what manifold, it all depends on what you are after. Smaller will give better low end, bigger top end.

That would be what I would do too. With the mech secondaries, if you find it is too big, you can always adjust the linkage so the carb doesnt open all the way. voila, effectively a smaller carb.

I'm still thinkin my 800 dp is the shizznit