Holley 390 and Offy Single quad intake questions

I'll add that anybody removing the exhaust pipe should consider drilling a hole and welding an O2 sensor bung in the exhaust while convenient. I put two in my slant exhaust, so I can use a wideband O2 sensor and calibrate it to a regular (on/off) O2 sensor. Simplest monitor is a little rich/lean indicator box for a regular O2 (Holley or MSD) and they are cheap used on ebay ($20). Even wideband O2 has become very affordable, especially used by tuners who are always upgrading to the latest. Easier and more accurate than trying to tune a carb by looking at spark plug tips.