vtapache,
I'm looking at the diagram in the '59 Parts manual and it does show (from the top down), a ball, a spring, and a screw under the hole in the main jet and power valve support. The grouping of the ball, the spring and the screw is listed as the 'valve unit, carburetor power '
It appears that there are two holes in the bottom of the support. The smaller one holds the metering rod jet. The larger one holds the ball, the spring and a screw/jet. Can't tell from the diagram if the 'screw' has a hole in it or not.
The parts manual lists carb repair kits for 57-59 Ser. 3-4-6 (6 cyl.):
use w/carb. 7003526-3863-64-65-3968-4468-4475-76-77-78-4495-4620-4915-5140-5921-22-5982-
7172-7180-81-9253-54-55-7013029-3953
Which I think translates into the following carb numbers being used on 6 cylinder trucks from 57-59:
7003526, 7003863, 7003864, 7003865, 7003968, 7004468, 7004475, 7004476, 7004478,
7004495, 7004620, 7004915, 7005140, 7005921, 7005922, 7005982, 7007172, 7007180,
7007181, 7009253, 7009254, 7009255, 7013029, 7013953.
