I think the Celestions are exactly why so many people are calling his tone "dull" these days. I would never put one in a tweed amp. Tweeds area already too midrangy to begin with. They need a speaker with more highs. Jensen C12Q or C12N are a much better way to go and is what most people use.
I don't use Twins or Bassmans. My only experience with tweeds is with my Victoria Double Deluxe homemade clone. (Basically a tweed Deluxe with four 6V6's instead of two, and with 2x12 speakers instead of 1x12.) Putting a 12AX7 in V1 doesn't give you that much more distortion and it takes away from the smoothness of the sound. Either a 5U4 or a 5R4 sound best in rectifier tubes. Yes, you'll get a little more distortion with a 5Y3, but not that much more, and you'll lose output power with one.
Believe me, if you put a 12AX7 in V1 and a 5Y3 in the rectifier socket, you'll have a very raunchy sound and almost no clean headroom at all.
Also, going the other way with a rectifier tube, using a 5AR4 / GZ34 will give you a ton of clean headroom, but you'll have almost no sag at all. Not conducive to great guitar playing.... The 5U4 or a 5R4 strike a very good balance.