I just recently stumbled across two NOS Caterpillar exhaust valves still in the original packaging plus wrapped in Cosmoline from a former US Military warehouse.  They have "Valve, Exhaust 1F3473" printed on them but also have the 4B426 part number hand written on the boxes.  Wondering if anybody can cross those numbers to determine what machine they fit? I'm trying not to completely unwrap them due to them being so well protected, but I'd guess they're in the neighborhood of D2 to D4 sized valves, but those numbers don't show up in any of my D2/D4 manuals.  Any help would be appreciated, thanks!

4b0426 does not show in NPR
1F3473 is exh valve for starting engine on D4600 and D318

4B426 shows as a tube fitting.

Thanks guys! Looks like these valves may be useful to someone that is rebuilding a pony for a D6 or #12 grader - appreciate the help.