Tim,I used dual Holley Webers on a moderately tuned 261 a few years back,M4F cam,Fentons,more compression.The stock main jets were fine,went up one size in the low speed or pilot jets to eliminate an off idle stumble.This was on a heated intake.I don't remember the main jet number,and I don't know if all the old H/W's have the same jetting,so try em and see if they carburate ok,I bet the main jets will be real close as is.
