independent of calculating the power output of a 2A3 at the operating points you describe---
the question of can the EXO-45 handle more than the nominal 2 watts we ascribe to the unit is the question of (perhaps) greatest import to you.
to make a long, long story a whole lot shorter--- our power rating is quite conservative--- and I generally like spec'ing conservative as this gives good magnetic headroom and allows the iron to operate in the region that we are aiming at...
however--- you already have the 045's in hand--- why not give them a try in the modified circuit--- worse case is that you would overload the outptuts and the tell tale sign of that would be a lot of distortion and just plain not very good sound. And it is likely only to occur (if at all) at the very, very lowest frequencies and at the maximum power levels--- so that if it begins breaking up simple solution is to turn down the volume.
But you might very well find that the 045's will just plain do fine with no change in your listening habits, volume levels, or etc.
You have the units--- why not just give them the workout and see (i.e., hear) if they work well in your app or not.
MSL
Builder of MagneQuest™ & Peerless™ transformers since 1989
