[SS Tim]

These numbers are for service replacement parts.
The applications are intended to depopulate parts inventories as much as possible by using one part number for as many applications as possible.

Parts manuals are easy to use if you read them carefully.

But don't expect a number in there to match a part you pulled from your truck.

Overall its real simple, the replacement manifolds at the time of printing (5/79) were:
3994045 LH
333846 RH

with A.I.R. this is the air pump for emission reduction
343787 LH
353030 RH

There is nothing there on that parts manual page to show application specific parts for a 396-402 C10-30 Air Conditioned vehicle. If there were it would probably be notated w/AC, C.A.C., or C60.