Ordered a set of Winged -C- 6L6s and that helped a lot. I have also been playing with the amp for a week. The treble and middle settings need to be run a little lower than I am used to. It makes the harshness go away. I was able to put the 12ax7 back in the PI slit and it sounded good too. I ordered another JJ 5751 and I'm trying it in the PI, as well. It may be better than the others. I'm not even going to try the 5R4 and 5V4 rectifiers that I ordered. The Winged C adjustment and getting a feel for the tone controls made a big difference.
Also, I was able to install the OT impedance tap switch after all.
So, pretty happy in the end. I'll keep playing it until the cab shows up. Maybe make some YouTube clips a bit later.