In the attachment you will find the (original) N12A schematic.
As you can see, they used 22 Volts for the filament and 155 Volts for the +HT.
Both voltages are on the high side, IMHO.
For the filament you want an output of 5 to 6.3 Volts. Nowadays we would use a LM317 for this.
Because after rectification and smoothing the DC voltage is higher than the AC voltage from the transformer, I would go for an AC voltage of 9 to 12 Volts.
The load of the +HT is very low, so a lot of energy is dissipated in the dropper resistors.
I think the best thing you can do is find a commercially available transformer, such as 2 x 6.3 V (in series) and 1 x 120 V (AC).