I don't know the exact specs, but your tech should be able to figure out something close from the schematic.
Assuming you are going to keep the dual tube rectifiers, then your transformer will need a 5 volt winding. Look up the heater current for a GZ34 rectifier, multiply it by two, and that would be the minimum current rating for the 5 volt winding.
The 6.3 volt winding has to supply 4-6650s, one 12AX7 and one 6AN8. Look up their heater currents, multiply the 6650 value by 4 and add them all together. That would be the minimum current rating for the 6.3 volt winding.
The power supply shows 510 Volts at the first filter capacitor, which is good as it makes the B+ voltage rating somewhat easy to determine. The 510 volts would be a peak-voltage (due to the action of the first filter cap), so you would want to determine the RMS value for the input to the cap voltage. Divide the peak voltage of 510 by 1.414, and you get 360 plus a fraction. So, your B+ winding would have to be at least 360-0-360, but considering there will be some voltage drop across the tube rectifiers, you will want to go higher to compensate. How much higher? Hmm... typically around 40 volts is usually dropped across a tube rectifier, but since the 2000s has two, that would be about 20 volts. I would be happy with 370 to 375.
As for B+ winding current... well, that's when I would get out the old transformer catalog, match up the above to find something close and then pick the one with the highest current rating... making sure I have more than enough current for the two heater windings.
Then I would worry if it would fit in the stock position!!
