Marty, as discussed here is my list of known C8A HUM serial numbers. If you have anything to add to this list, please do.
Brian Gough may have more info too, have you asked him?
Chassis model | Cab Model | Chassis serial | Engine serial | Order no | Date of mfg | Vehicle model | Body Model | Body serial | Chrysler Serial-no | WD census no. | Source
C8A | 13 | 3844515289 | FR3918642 | LV.1697 | AUG. 12/43 | C.HU-441-M-PERS-1; 2nd plate: HU441-M-MACH-ZL-1 | 1C1 | 3924 | MACH-ZL-1-068 | ... |
http://www.mapleleafup.net/forums/sh...ght=3844515289 (Marty Morren, NL)
C8A | 13 | ... |... |... |... |... |... |... |... | CZ4210145 |
https://flic.kr/p/pkDhQh
C8A | 13 | 3844536668 | FR3969158 | LV.2611 | MAY 11/44 | ... | ... | ... | ... | ... |
http://www.mapleleafup.net/forums/sh...36668#post9656
C8A | 13 | 3844536670 | FR3969311 | LV.2611 | MAY 11/44 |C-8A-MACH-ZL-2 | ... | ... | ... |... |
http://www.mapleleafup.net/forums/sh...670#post174430 (Pieter Bergman, NL)
C8A | 13 | 3844536671 | FR3969368 | LV.2611 | MAY 11/44 | ... |... |... |... |... |
http://www.mapleleafup.net/forums/sh...671#post129049 (Mark Coombs, USA)
C8A | 13 | 3844536688 | FR3969099 | LV.2611 | MAY 12/44 | ... |... |... |... |... |
http://www.mapleleafup.net/forums/sh...36688#post9656
C8A | 13 | 3844536691 | FR3968926 | LV.2611 | MAY 15/44 | [plate missing] |1C1 | 6443 | ... |... |
http://www.mapleleafup.net/forums/sh...ght=3844536691 (ex-Shayne McGuire, CDN - current location u/k)
C8A | 13 | 3844536696 | FR3969103 | LV.2611 | MAY 15/44 | C-8A-MACH-ZL-2; 2nd plate: HU441-M-MACH-ZL-1 | 1C1 | 6448 | MACH-ZL-1-087 | ... |
http://www.mapleleafup.net/forums/sh...ght=3844536696 (John Corden, UK)
Notes on data sources:
This information comes from the data plate on top of the dash, as fitted to all Chevrolets:
Chassis model | Cab Model | Chassis serial | Engine serial | Order no | Date of mfg

The Vehicle model plate left of data plate on dash:
Vehicle model

Note: some have a second plate attached to the left of the Vehicle model plate during the conversion to HUM:

The Body plate on rear of body - this plate was added to all C8A Heavy Utilities:
Body Model | Body serial

The Chrysler plate on rear of body - this plate was added during the conversion to HUM:
Chrysler Serial-no

The Number painted on the door:
WD census no.
And Information gleaned from an open source (most often this Forum):
Source