They don't need to be quad-matched for rectifiers. You can even have all three pairs in a triple be of different color codes, as long as the inners match each other, and of course same goes for outers and tweeners.
Furthermore they don't even need to be of the same tube model, only within the same tube family.
For example you could go: (from the rear view)
red 440,,,,,,blue 445,,,,,green 420,,,,,green 420,,,,,blue 445,,,,,red 440
Just keep in mind with the MW triples that it is those in-between slots (blue 445 in the above example) that are fully engaged when in the 50w setting.