I would say that the 1mA or so of current through the balancing resistors is insignificant. You could use a 100uF 500v capacitor instead, but it would probably cost more than the two 250v ones.
The 6N1P is very different from the 6922, apart from having the same pinout. It has much higher anode impedance and likes a higher voltage. It looks more like a higher-gain 6CG7 substitute to me, but does not sound anything like as good. I'd stick with the 6922/E88CC.
Edit: You will need to check that the 6922 can provide enough voltage swing to drive the EL34 without distorting.
