On the List#1273-1 (ECZ-AD) carb I have sitting here, it has a #1584 primary metering block and a #1589 secondary metering block.  My Holley parts catalogue verifies that the 1589 secondary metering block is indeed correct for this carb but the listing for both the list #1273 and list #1273-1 carbs has a blank for the primary metering block.  But I’ve no reason to believe that the 1584 primary metering block is not the original for this carb.  Hope that helps.

Lorena, Texas (South of Waco)

Come on guys! somebody must have an answer to my question, On the 1957 tbird 312, the carb from the factory was the holley 4 barrel, list 1273 ecz-AD Can anybody tell me what the numbers on the metering blocks were? from the factory. I am waiting for word from Holley but they are taking their time.

Thanks