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
Yes. I found the stock genelex 12at7s a bit grainy compared to the mullards I have in there now (cv4024). Also RCA 12sn7s from Brent jessee (not expensive) made an improvement too but I’m still evaluating that.
modern day chinese or russian small signal tubes are often quite bright and strident compared to old stock counterparts from usa europe or japan