Tar mate ,,, you obviously know more bout this than me but I think messing with these things can quite easily end in tears for the novice ,,Unless (like you) You know how to read between the lines and bring it all together.
Myself having been on the (I would not have a friggin clue how a valve amp works) End of these things I can clearly see that it can be very misleading when some half witt guru geek says,, oh you can turn any amp into a marshall,,, just add water and smoke some RockNRoll weed and then anything sounds wonderful.
(Adding also,,,Make sure the Valves have Gold print and are at least 60 years old
I would erk at the idea of altering any kind of old Bassman Amplifier when it makes more sense to sell it and purchase a Marshall instead
(Do we have a dumb dumb emoticon?)
Interesting that you mentioned output transformer as well,,,,,
Yes I agree!! They are different and DO alter the Final outcome.
cheers mate,,, Phil.