I know there should be schematics somewhere, I'll have a look in my computer too.
The big upgrades however are not on the schematics (except for the 1.0 to 2.05 update which involved some hardware too).
They are simply:
- MDRT
- Standard noise mod
- High quality tubes
- Replacing the opamp by a BurrBrown of the same type.
For the rest the MB-1 is already about as perfect as it can get