Has anyone modified the Class A Music Hall Mambo?

I'm just starting to think about modifying this amp.  I picked it up at a great price.  It's 50w all Class A and is 50 lbs.  The build quality is excellent.  I'm going to have some fun trying to squeeze out as much as possible from this amp.  

Underwood HiFi and Parts Connexion have offered mods for $1,600.  https://www.underwoodhifi.com/modifications/mambo

Has anyone hired out or DIY'd modifications to this amplifier?  I'd love to get/share ideas. 

I cannot get a hold of a schematic--unfortunately.  Roy Hall doesn't have any left.