My '63 K 10, # 129***, from St Louis Plant is a Second Series and has the 292. Trucks 118545 and later from St Louis are "Second Series", 118544 and lower are "Firsts". Similar for all of the other plants, as shown in the parts book noted below.
Because of differences in assembly, six cyl engine perch design and location, for example, and I think cab mounts too? and probably others, these changes to the assembly line would have been planned well ahead of time, not when they happened to run out of engines . Anyway,
The Suffix info is on p.46 of MSA-1 Chevy Inline 6 Engines Casting Number and Code Guide.
1963 Series Info is on P.14 of GM Parts Division '46-'72 Chassis and Body Parts Catalog for Chevy 1/2 thru 1 ton trucks.
My 1963 truck Heritage package was the least informational one of the several I have purchased
