Well, you could.
I would buy 5 and stick them in. Transistors have such a wide parameter spread matching would be a waste of time, and if you are just going to judge them by ear - why bother. Your ear (as well as mine and 99.999% of people on this planet) won't be able to tell any difference. Perfect matching is only good for Hi-Fi anyways and a Concert ain't a piece of Hi-Fi equipment - it is meant to produce a sound, not to reproduce a previously produced sound perfectly.
I said 5 because if I have to replace one, I replace them all. New micas and grease as well. The 5th is the transformer primary driver operating in class A, but you already knew that.
Replace them only after replacing the other components, like caps. Otherwise you could wipe them out and wind up replacing them again. Lucky they is cheap!!
And give the amp a good dusting out because dust accumulations after years can get to be real foul smelling if not downright conductive. Check the thermal cutout also - clean it and re-grease. If you don't solder the lug connections between everything, give them a real good cleaning and re-tension the connections.
Good luck!!