I never built this with 12B4 and CCS, so I don't know what the gain *MIGHT* have been. It has a 50k volume pot with a 75k shunt resistor so it is gain-reduced anyway.

Don't worry too much about the B+, with 10k plate loads, there is no dissipation issue until it's over 400 anyway. 4 or 5( or maybe 6 ) LED's will be fine too. Just make sure your plate loads are up to the task. Remember, the output voltage is going to be less than 10 p-p, so we don't need a lot of cathode bias....back to less LED's no?
cheers,
Douglas