Altair 8800b-PS question. Upgrade kit serial numbers?

[TJ_Mossman]

Hi all, I've recently acquired an Altair 8800 with a PSU from the 8800b. According to the July 1976 Issue of Computer Notes, there were a few upgrade options for existing 8800 owners.

8800b-U (kit only)*

The 8800b-U will update the 8800
to. the 8800b. The only items not
included in this package that are
included in the 8800b are the
switches, LEDs, case and motherboard.

8800b-SL (kit only)*

The 8800b-SL is a further update to
the 8800b-U and contains the
switches and LEDs for the 8800, to
duplicate the 8800b switches and LEDs,

8800b-PS (kit only)*

The 8800b-PS is for those desiring
the power supply modification but
not the 8800b -U in its entirety.

My unit is marked with a 54xxxxxK serial number, normally indicative of the 8800b kit. Did these upgrade kits have serial numbers, or is my unit made up of donor parts?