Expand the below quote from myself.
Its not a spread bore with a small difference in sizes between the primary and secondary bore but the huge difference between them. See the TQ below.
The industry made this distinction decision long ago.
The secondaries are spread out wider than the standard square bore intakes would allow the carb to be bolted onto the intake. They had to spread the secondary bore to meet the more spread out width of the secondaries of the new carbs. The QJ & TQ. Holley also has spreadbore carbs like below in vacuum & mechanical secondary. 4160 & 4150 styles as well as the defunct two piece design now carrying the Summit logo. Those were the 4010 & 4011 series carbs, FWIW. They were good units.
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