I have a 1987 Ampeg catalog and a 1989. The '87 is pre white piping and it shows 27 inch width on the smaller cabs (the 810 is 26" wide) - the '89 catalog shows white piping and 24" wide bass cabs. I also have a 1984 SVT brochure (MTI era) - it only shows the head and the 810 cab - but it has a price list (pictured) with it. The price list is interesting as it shows a 2x15 cab - which may be these?: Unusual Ampeg B25B cabinet sighting
Ah ha! Very interesting price list, thank you. And a slant-front 410! Maybe those mystery cabs are B300's. I wonder exactly what years the Ampeg-Altec connection was. I can't find squat on the interwebs about the B300. I think I'll start a B300 thread.