This is quite interesting to read. There are modern BJT transistors that fall within the specs of older transistors but are much more linear. MJ21193 and MJ21194 for example. but I agree with the earlier responder. The replacement transistors have to have similar specs compared to the transistors being replaced. The designer actually designed the circuit with particular transistors in mind.
but, amps like Bedini, Threshold, Mark Levinson (the older ones) can all benefit from upgrading of driver and output transistors to newer more linear ones. specifically, MJ21193 and MJ21194. keeping in mind the driver transistors also.
much, much better sounding amps.
Get the spec sheets or spec books on the transistors and the newer ones
Over the years I have obtained many, many transistor spec books and spec sheets. Because sometimes it is simply impossible or impractical to obtain or use older transistors. Same power bandwidth, hfe, vbe, etc. but much more linear.
enjoy