[bikerhifinut]

I'm going to play a bit of devils advocate here Andy so please take this in the spirit it's meant.
3 pairs of EL34 in parallel, for starters thats a hell of a brave thing to do, 2 pairs could be challenging enough!
So.
If you want to persist with using 3 pairs of El34 then why not run them as individually cathode biased valves, you'll still get 25 to 30W per pair (you can squeeze more but these are realistic achievable targets) which adds up to a stonking 75 to 90W and I don't think unless you want to light up an auditorium that you'll notice the difference betwen that and 120W. Your ears will have been bleeding long before that in any normal to large sitting room.
There are a lot of advantages to this approach.
Not least of which, you'll be running your expensive power valves nicely below their limits. Right now you're squeezing their poor little spheroids rather hard. Not at all necesarry in domestic audio, we aren't amplifying a rock band here.
Ok.
Now another curved ball.
for an amp and a half less heater current you could run a quad of 6550/Kt88 or equivalents there may even be some cheap telly valves that would respond to this,I don't know but others will. I stick to mainstream Audio valves as they are mostly still manufactured somewhere and dont want to upset the guy who might want a PL something or other to keep his 405 line telly working.
Ok so why do that?
You'll get 100W with cathode bias and an HT of 500V without breaking yours or the amps sweat. Or an easy 70W at around 410V Ht.
Of course I do not know what your output transformers are rated at in terms of a to a resistance. That will rule the valve lineup.
However those big well built transformers now in your possession will handle 100W and are well suited to a quad of KT88 etc.
Like I said, these are only my feelings and I can see you are riding a steep and exciting learning curve.
i've spent too many years noodling around with valve power amplifiers and have come to the conclusion that in the average UK living room it simply isnt worth trying to improve on the classic circuit configurations, the gains arent audible. Better invest in the absolutely VERY BEST output transformers you can find, this is an area where mostly the ancients had it nailed. (Theres a couple at least on here who understand the Black art of transformers).
Then build the neatest and well laid out circuit you can, using the reliable high tolerance and high stability passive components that were'nt available even as recently as the 60s or even 70s for some bits.
Don't even think about valve rectifiers, but you know this.

And if after all this, you continue on your journey of self flagellation, I'll be there with what encouragement and very limited help I can give.
Because at the end of the day I know why you are doing it. But don't get disheartened when things don't work out.

The other Andy.