What size jets in Rochester 4GC
 

Anybody know what size jets should be in a Rochester 4GC carburetor on a 327. My carburetor, although about the same vintage as my truck, is not original to my engine. My carburetor has size 60 jets in the primary and size 66 in the secondary. With this setup I am only getting about 9 miles per gallon. I was thinking I might be able to go down a few sizes and improve my mileage, but thought it might be a good idea to find out what size jets should be in the carb in the first place.

thanks