Holley Metering Block ?

Doh! What was I thinking? Of course the center carb has a block.
No theyre not all the same. The 1850s for instance are different from the 3310s.There are several/many different calibrations.I think I have 4 or 5 different blocks in my collection,not including the ones Ive recalibrated.Mine are all interchangeable. I have 2 carbs with 5 or 6 digit list numbers that I havent tried.(I think they start with 80xxxx). They are very lean.