If you used a chart from Holley for instance to estimate CFM requirements,that would be a 4bbl.My 261 is equipped like yours,a 390 Holley 4bbl is just right.The Holley Weber,32/36 flows 280 CFM according to my Holley specifications manual, that's 200 cfm as like a 4bbl,not enough, 2 of those carbs works well.
