Just a comment:
Tuning ANY single carburetor to run WELL at both 5500 and 8500 feet is going to be exceptionally difficult, if possible at all.
As a general rule (remember that "general rules" were made to be broken by us privates
) single carburetor calibration would be along the lines of:
Sea level to 4000 feet - standard calibration
4001 to 6000 feet - 1 size lean calibration
6001 to 7000 feet - 2 sizes lean calibration
7001 and up - 3 sizes lean
This gets even more complex when one adds an unknown quantity of ethanol to the fuel.
(Opinion, others may differ) The easiest way to approach this issue would be either:
(A) A single Carter AFB 750 CFM carburetor part number 4760s, modified with Pontiac profile rods, jets, springs and auxiliary air valve.
OR if you like multiple carburetors:
(B) Two Carter AFB 625 CFM carburetors part number 4759s, modified with Pontiac profile rods, jets, springs, and auxiliary air valves.
The reason for using the Carter AFB's is simple. One can dial in the carburetor(s) at the altitude where the truck lives, and then acquire custom rods to change as one drives to different altitudes. The rods may be changed without removing the carburetor or even removing the top. To prove a point, I once changed a pair of rods on one of the AFB's on my shop truck with the engine running. I don't recommend this practice, and only did it to prove how easy it was to change the rods.
As Joe mentioned, going to be virtually impossible to dial in a tripower on a 455 unless you have the 1966 manifold with the large center. Even so, the easiest way (and the least expensive way) to tune for multiple altitudes would be to acquire two or three center carbs, dial in each for a different altitude, then swap the carbs as needed.
Jon.
