If it helps (and it probably doesn't), the assembly AS605FH2 is shared with the 14-1/2" lathe, in case you find someone parting out that size. But those were much less common so it's a long shot. It's good to be able to interpret those parts lists, though. "FH" means "for both 14-1/2 and 16 lathes". F was the code for 14-1/2, and H the code for 16. "AS" means "assembly", and that includes the needle bearing (PT384FH) and the gear, per the parts coding.
More potentially useful: The same idler gear and bearing (AS605FHn, where n is the version number) is used in the double-tumbler gearbox, for both tumblers. I have not found that changes in the version number prevented me from installing a part, but I'm sure that's not a universal truth.
The 153x12 (your "253" is a typo) is listed under South Bend Form 1178 "Commercially Available Hardware" as a 1/2 x 2-1/2" steel dowel pin. Those are available from McMaster, among others. In the double tumbler gearbox, the dowel is only slightly different--it's designated 160x254, but that is a "steel pin" that is 1/2 x 2-1/4", which is the same as used in the single tumbler but a quarter inch short.
Rick "who has been searching for 14-1/2 parts a lot lately, and has sort-of figured out the parts coding" Denney