Probably a variation of the old Ampeg Big-M 1x15", but with added reverb; the bulletproof transformers are no surprise - IME old Ampegs are some of the most reliable amps out there - which also IMO suggests a 20-30W Class-AB topology, but the move to 12A-7 type tubes is definitely rooted in post-1964 Ampeg technology (my '64 Rocket uses 2x6SL7 octal preamp tubes)...
Don't sweat the pics - although greatly appreciated, you provided
plenty of information...
