Mark IIB Preamp tubes

Hi guys.
Can anyone tell me what the original preamp tubes Mesa would have shipped the Mark IIB with please?
This is a Non reverb model so 4 x 12ax7's.
There were 4 x GE 12ax7/7025 in it but they're Fender "Special Design" Labeled?
Would Mesa have used Fender labeled tubes or are these likely to have been replaced?
I'm on a quest to have this amp as original sounding as possible as the day it left the factory.(A bit OCD that way)
I got some NOS Sylvania 6L6GC Power tubes and the GE 12ax7's seem a bit weak now?
I've got current Mesa 12ax7-A tubes in there now and although it sounds quite nice on the clean channel I'm not to keen on the sound of the lead channel.
I want it to sound thick and creamy with lots of sustain,not buzzy and thin?
I've heard it sound like this years ago so I know it can!
I would really appreciate help/advice with this.
I take it I need to go the NOS route if I want it to sound as it was meant to sound?
P.s Can the GE tubes be weak and affect the tone/gain of the amp even though they still function and dont present any noise/microphonic issues?

I can't help but my 1982 Simul-Class Mark IIB combo could some help in the gain department also.

I have a fresh set of Mesa tubes in my amp, great cleans but not so great overdrive at least at lower volumes.

Hope someone in the know responds to help us with overdrive issues witho a MKIIB.

"I want it to sound thick and creamy with lots of sustain,not buzzy and thin?" I cant tell you what Mesa used originally,but I can tell you what worked for me in this area in my MKIIC+.As you know mesa gets most of its overdrive in the preamp.The preamp overdriving tends to be very buzzy and when pushed too hard can get thin and nasally.I replaced v3 and v4,which control the lead drive channel with 5751's.These tubes have a bit lower gain than the 12AX7 and a somewhat softer high frequency response with a strong mid range.I also rebiased my power tubes to have a higher current draw than Mesa sets in their amps.The results were fantastic.I can set my lead drive quite high and not get that ear splitting high frequency buzz,it has a rich full mid and solid bass.I describe the overall tone as "creamy".I have done this for customers in MKII's,III's and IV's with similar results.I use only NOS tubes,I have over 100 NOS preamp tubes in my personal stash I have amassed over the last 30 yrs or so and can tell you the new production 5751's dont come close.I have had clients try them and they went and got old stock after trying mine.If I remember correctly,you still have some unresolved problems with the tone stack in that amp,no? With that being the case,I dont know if you should,at this point, be chasing preamp tubes just yet.

you still have some unresolved problems with the tone stack in that amp,no?
Yes Stokes.
I've spoken to Mesa about the issues with this amp and Mike B has suggested having the volume 1,treble and lead drive pots measured to see if they are in spec.He said he has seen some of the 1m pots to be well worn out to several times their original value and has found a few treble pots that have went out by as much as 400k.
So this is what I'll be having checked out first.Then I can see how things go from there.