Do you have a question you would like to ask us?
Let us know what it is in the “Ask Offenhauser” section.
If all three of your carburetors are 3-1/4″ X 1-7/8″ (which is the small base) you will need part number 4060 drilled for the small base Rochester carburetors.
As for the other manifolds you reference, 5257 is for three (3) Rochester large base carburetors and 5257-TP is designed to use the GM factory style tri-power (which is why it has “TP” in the part number) carburetors which consisted of a small base 2GC as the main (center) carburetor and two (2) large base carburetors for the secondary (outer) carburetors.
I do not have the number of a Seattle dealer, but White Owl Speed Equipment does ship nationwide. You can reach Dan at 559-786-1864.