Speaker brand used in Kustom combos
..........S.N....Amp Prod Date..Speaker Brand Used
From .. 44800 ..Sept 1969 ....Eminence speakers
To ..... 54000 ..Mar 1970 .....Eminence speakers
From .. 55000 ..Apr 1970 .....CTS speakers (also Jensen on some K150 combos)
To...... 86000 ..June 1972 ...CTS speakers (also Jensen on some K150 combos)
From ..87000 ..July 1972 ....KEI (Kustom-Eminence Integrated)
To ...112000 ..Dec 1973 ....KEI (Kustom-Eminence Integrated)
CTS speaker with hole in center cap like Eminence
Now, check out the ebay ad “Kustom 10 speaker”. They came in a Kustom amp (could be a K100C-8 2x10). They are CTS but the chrome voice coil cap has a hole in the center like Eminence. They are 16 ohms each and are wired in parallel.
The newest of these two is 137 7011 so if you add some time for shipping to Kustom etc they could have been installed in a Kustom amp around SN 52700 say March 15, 1970.
Note that this is around the time that combos transitioned from using Eminence speakers to using CTS.
My guess on what happened here is that possibly CTS was just getting started producing speakers for Kustom and was not using the solid cap yet. Or possibly it was part of a pre-production test.
Another mystery is why these two were 16 ohms wired in parallel, as many of the 2x10's in this time period with both Eminence and CTS had two 8 ohm speakers wired in series.