I thought that it was three channel also,,,, a previous poster (Post 2) thought it was half (of a two cabinet stereo set), with a 2nd amplifier in the missing cab... the last picture in the 1st post, shows a big (12-15") center speaker, with a 6x9 mounted on one side and a cutout for another on the other,,, you can just make out a magnet, it seems, under the cutout,,,, speaker must be on the floor of the cab...
I'd count the output transformers on the chassis you have, if there are 3 of them its all on one chassis, if only one or two, an extension cab is missing for stereo...