Use this formula for a guideline. I will amaze you how small a carb really needs to be:

CFM= CIDxRPM divided by 3456xVE

CFM = Cubic feet per minute
CID = Your engine's cubic inch displacement
RPM = MAX wide open throttle RPM, i.e racing. As a daily driver - the engine needs are much less
3456 = a constant
VE = Volumetric efficiancy. A stock engine is about 75%, mildly modded, 85+/-

An example(my engine):
CFM = 302x6000/3456x.85
CFM = 616 cfm.

Since I will seldom see, if ever 6000 rpm, I have a 600cfm Edelbrock 1405, modded to electric choke - and it does run very nicely

The Performer carbs absolutely do NOT like dirt, so a very good filter should be used

Glenn - very nice write up. I don't have a late IB, so am surprised the Endurashine is jetted so lean.