The ‘Guaranteed Venues’ mixers were just standard 828 mixers but with the customer’s name silk-screened on them. We built about 20 mixers for that outfit, and as a concession we put their name in them. There were a few small modifications on those mixers….. we made provision for blanking plates to be fitted over the rotary controls to stop people fiddling with them! But to answer your question, they were standard 828 mixers. 
