Okay, this is getting to be a very educational thread!
Now here is a different angle.
This carb on ebay (
web page ) is an autolite off an earlier 289. Were these Holley 500 carbs?
Doesn't it flow at around 350 if measured like a 4 barrel?
Would it be a good choice for a 250 with mild cam, ported, 1.6 exhaust valves, and a few other goodies?
Bob