Slow blow elevated reference potential

http://www.qsl.net/sv3eao/1/MySlowblow.zip

I'd like to go for 6.3V heater power as I'm going to use 6SN7 as input tube. Is it enough to change heater psu
to output 6.3V or I have to change something around that floating ground circuit as well? If so what needs to be changed? I understand, roughly, what it does but I'm not sure about the math of it at all...Or shall I run the heaters in series and leave it as it is?
Thank you


EDIT: wrong link

This elevated reference potential is made to not exceed maximum heaters to cathode voltage (see 5687 datasheet).in this example, SRPP,with heaters floating at a given potential, voltage difference between them and the cathode of the top triode does not exceed this limit, and still stays close enough to the the potential of the bottom triode. It's as simple.
So, to answer the question, you absolutely can make  the same thing with 6,3v and leave everything else as it's in the schem.

Laurent.

Laurent, thank you very much.
Milos