OK Mark, the short answer is no, any 6L6 variant will plug in and play.
Only JJ 6V6's have the balls to handle the higher plate voltage, so be careful there.
Ok when the final stages of design on the Therapy were taking place, I always play tube swapper.
I tried 13 different pairs of 6L6's in the circuit.
A variety of NOS 6L6's to the old wafer base Russian 5881.
A couple of things stood out on the JJ's.
Wonderful sweet upper end, chewy mids an a stout bass.
Nice rich cleans and a very smooth overdrive.
Also the JJ builds some of the most reliable tubes today.
They are easy to source, readily available, moderately priced , and come well matched.
Yes sonic details are very important , but as a manufacturer other issues hold as much weight in my selection.
Z