So the schematic that was posted shows 515vdc at point A. If this is correct, then the transformer would be 515*0.707 = 364 vac (assuming no load). I think the 350/0/350 would be just fine as tubes will work over a wide spread. However that first cap is shown with a working voltage of just 350vdc - way too low if indeed the voltage after the diodes was/is 515vdc. That cap's working voltage is too low if the transformer puts out 290vac, which would give about 410vdc across that cap.