On the TO3, I mean that quite seriously. I can’t remember the last time I saw anyone use a TO3 in a production design. Your idea of plentiful and cheap is likely different from mine. I don’t buy components off EBay unless I am finding something obsolete. You can find the odd TO-3 in stock at stocking distributors, but they are a rarity these days and legacy devices.
If you change the output stage, bias circuit, and the drive circuitry before the output stage, which means 2 stages of what is likely a 4-6 stage amplifier (and likely feedback to account for different bandwidths), then it is not the same amplifier any more. You can’t change 33-50% of an amplifier and say you are just comparing the output devices. Yes end of story. Your claim that this allows you to simply compare output devices is not true.
If you change the output stage, bias circuit, and the drive circuitry before the output stage, which means 2 stages of what is likely a 4-6 stage amplifier (and likely feedback to account for different bandwidths), then it is not the same amplifier any more. You can’t change 33-50% of an amplifier and say you are just comparing the output devices. Yes end of story. Your claim that this allows you to simply compare output devices is not true.