It would be all too easy to change to a cascade HT supply. And in some aspects a cascading HT is a better way to do things as any failure (burn out) of any of the supply components will effectively kill the V1 tube thus stopping the amp from trying to do anything....

BUT ...

Part of the charm of a VOX amp is how it breaks up with increasing volume/gain.... and I think the HT arrangement is integral to that break up behaviour... So therefore in my build the only significant changes to the HT config will be the use of a Marshall 18W power transformer (which isn't very significant as the HT voltage and currents are very close), and solid state rectifiers instead of a tube rectifier.