Tube rolling LTA MZ3

wondering if anybody has done any tube rolling with a LTA preamp? Just got one, my sickness immediately makes me wonder if I can make it even better! Anybody have ideas on weather the 12sn7 or 12at7 position would have the most influence on sound?  For me, (in my system, my ears) this pre is an upgrade from Pass Labs XP12. So much more dynamic and engaging.
thanks for any perspective, Ted
modern day chinese or russian small signal tubes are often quite bright and strident compared to old stock counterparts from usa europe or japan
You can also use the 6SN7 but make sure you move the jumper.

LTA does include NOS tubes with their full size Microzotl preamp and they are usually GE or RCA. I found these tubes sound great and can be found without taking out a second mortgage.

From my rolling, the circuit was far more sensitive to the 12at7 than the 12sn7 and the stock small tubes exhibit glare. 
I love my Microzotl preamp. Prior to this I has a Decware CSP3 with all the upgrades. Got the upgrade itch and tried the original Schitt Freya after reading all the great reviews. Kept it in my system for several months and rolled quite a few 6SN7's through it. Fortunately I owned a few already as my Melody M845 amps use them as well. I never could get the Freya to sing for me. Wanted to like it but just didnt have the synergy in my system I guess. I finally popped the Decware back in and the magic was back. 

The upgrade itch caught again last year and I bought the microzotl pre. Right out of the gate I new the Decware had met its match.

I've rolled quite a few tubes through the microzotl when a pair of the legendary Melz 1578 hole plates came up for sale from a reputable seller. I have a pair of these in my stash and they were the best 6SN7's I had ever rolled in my amps. Unfortunately one of the tubes started to crackle after a few months and I needed to retire them. Before I purchased another pair I figured I would throw them in the microzotl to see if they were a magical as I remembered. Low an behold no crackle. I popped them back in my amps and the intermittent crackle was back.

The Melz are now running full time in my Microzotl with a pair of Telefunken ECC801s in front. For me this combo is magic. 

The main point here is not to convince you that you need to run out and scour the internet for these rare specimens as much as the Microzotl runs tubes at very modest voltages. If you are like me and have some tubes that have picked up that all to familiar popping  / crackle sound consider giving them a roll. YMMV.