The truth is if you have a quality design schematic from the 70s, and use parts from the 70s, you will make a good amp.
Modern parts, what you might think of as high end parts today, when it comes to the transistors, today, they have been optimized for switching performance, not necessarily linear drive. This can alter the sound, quality and steady function of the amp which was designed with 70s transistors in mind.
When it comes to resistors and caps, you have a much better selection for resistors. With today's caps, if you need it, the higher quality ones will cost you money. The life of these components will be better than the ones from the 70s if you pay for the good ones where needed. Be careful of any cap which needs to handle high ripple currents in your design, the odd high end ones from the 70s will need high end ones from today as well.
Make your PCB with 2oz of copper at least. Old 70s design PCBs had no soldermask and usually flooded the traces with solder to thicken them up to handle higher current where needed if not everywhere.
Everything else is BS. Good luck, rejuvenating old analog circuits from the 70s will be a fun experience and if you choose the right design, don't believe anything said above, and don't strive for that absolute minimal distortion, the design should sound perfectly fine.
As for transistors, motorolla/On semiconductor still makes a nice NPN/PNP matched pair designed for linear operation for servo motor and HIFI audio in a TO247 package, designed to maintain at least 100 watts continuous on a generous heatsink. be careful as Chinese crappy knockoffs exist.