I would not mod the amp or replace parts just because they're old*. You've already said you'd pit it against any Fender. Count your blessings - you've scored a great amp! Start with basic maintenance and proceed with repairs if needed. Clean and re-tension all of the tube sockets. Clean the pots. Tighten screws. Reheat any cold solder joints you see. That might be all that it needs. Enjoy the tone! * Couple of caveats: I'd consider installing a three prong power plug. And I'd probably replace the power supply electrolytic caps if they were 40+ years old.