I’ve never tried a 6L6 with the metal case. Pin 1 on V2 (the power tube) is connected to ground in a Two Stroke so you can use a EL-34 type tube. The 6L6GC and 6V6 don’t use pin one. On the 6L6 (metal case) pin 1 goes to ground so I’m guessing you can use it without issue.

I’ve tried most of the tubes you listed. Tubes from different manufacturers can sound very different. The KT-66 (Electro-Harmonix) I’ve tried I found to be harsh and not as pleasing as a good 6L6, but they are a little more powerful.

I talked at length to the JJ factory rep recently and he said their E34L is about 20% more powerful than their EL-34. I did not care for the JJ E34L that much, it was not nearly as sweet as a JJ 6L6GC. I just got a JJ 6550 (big and pricy) and am looking forward to trying it in a Two Stroke. JJs are my favorite new tubes because they tend to be rugged, sound good and are reasonably priced. I think a good JJ 6L6 is hard to beat in a Two Stoke.

NOS tubes can be great (or not), I especially like a good NOS rectifier tube in the Two Stroke if you are going for a browner tone because the NOS 5Y3 tends to run about 40v less than a new tube (like a Sovtek)