[Arran]

From what I recall A 6Y6 gas a lower maximum plate voltage, 200 VDC, but draws more heater/filament current then a 6V6, 1.25 amps verses .45 amps for the latter, so the net result may be that the heater voltage might be slightly higher for the whole set. I think I would just procure some more 6Y6s, they are not a particularly expensive tube. From what I read the 6Y6G was developed for use in TV sets, one of the first specifically designed for it prior to the war, but I have only found them used in a handful of radios, one being a Canadian Westinghouse 754, another being a U.S General Electric H-116, I have a feeling that your Westinghouse might be similar to the H-116 other then the choice of a 5U4G rather then twin 5Y3s like the G.E has.
Regards
Arran