make-over for amp.

Do you mean changing/upgrading components?
I wouldn't do that!
I would assemble another system instead and keep it running as-is.

Parts?
First-off, having an equipment that hasn't played for almost decade, I'd take off the covers and clean the circuit boards with soft paint brush preferably outdoors.
Second I'd give it a basic service:
Inspect with monocular and fix bad solder joints starting from the high voltage domain. While doing that you can also inspect the shape and values of the DC electrolytic capacitors that are very vulnerable to aging and loosing its discharge capabilities. I'd replace them all with corresponding Black Gate ones but size should be considered to fit onto the circuit board.
It's not neccessary to be an engineer but experience of a tech is pretty much desired.
Engineers exist to create problems and Techs exist to solve them:-)
As to semiconductors, they become better and better each single day hence there's a possibility to replace existing ones with same peak-Vcc and Hfe but better and more linear current characteristics... This indeed requires acceptable knowlege of semiconductors.