The Twin was originally intended to be a pedal steel amp. Subsequently upgraded to the dual 15 Showman. Fender never expected guitar players to be that loud.
Then the CBS engineers came in and tried to make them hi-fi amps and even cleaner. Which almost killed Fender.
I'm not sure why someone would want to optimize the cleanness of one unless it's for a pedal steel or something other than a conventional electric guitar. Sounds painful to me. I'll let our resident Fender expert Bob fill in the rest of the particulars.