iirc Sound City speakers were Celestion - I did have an old pair of "upright" styled cabs with the open slot down the back - got them when I bought a PA cheap and used the head as my bass amp for a while until I blew a transformer - then got the Hiwatt and used them with that until they died, also used a WEM 215 with the Marshall...
I've predominately used guitar speakers, the Celestions that are in the cab are guitar speakers, afaik, but when I strip the cab down I'll post a pic or two, I guess...
Dave (Mr Hiwatt - RIP) Reeves used to be employed by Sound City, which is why there is a similarity in design between them and the Hiwatts...
Just as a point re the instrument and pups, I used to be running the Thunderbird with a Peter Cook Custom pup and a DM MB1, and a pre-amp I built myself from some old plans, so it did "bark" quite a bit, and the RDA with all the bells and whistles until they burnt-up on re-entry, so I did push them...
I will eventually post some stuff - there are some studio recordings (4) I made with the Peter Cook in '88 that were recorded DI which will give a reasonable impression of her sound, plus some (dodgy) video I got from this year to give some before/after comparrison - something I'll do in my "spare-time..."
I'll also post the fretless RD for a sound image, too...