The 400VDC coupling caps in the PI are a bad idea. Mesas fail all the time because of this. 630VDC will be better.
It's because the -bias voltage is cumulative with the positive plate voltage. The cap 'sees' both these voltages added together. So if we had a -50VDC bias voltage and a 250VDC plate voltage on the PI, those caps would be 'seeing' 300VDC. Then factor in, when the amp is unloaded, those voltages can be higher.
I also think trimming up the values there could be a good idea. Gets rid of flub and blocking distortion.
It's true i've lost my marbles and i cant remember where i put them