Just checked the V55 schematic you posted.
A VERY good amp, very much doubt doubt you can "improve" it.
Of course, you can mess its sound easily
You want the best you can get from it?
No need to electronically modify anything, just:
1) plug it into a 2 x 12" loaded with V30 or G12H30 or 4 x 12" loaded with any od those mentioned, *or* Greenbacks or Jensen C12N or MOD 1270 .
All KILLER speakers.
2) put the Master on 10 and leave it there forever.
Raise the clean volume until it just starts crunching and the drive gain so it distorts the power amp as much as you want.
You can add a clean boost pedal for soaring solos.