Px4 & 101d replicas. If 300B allowed (cant recall) then as a value play, try the PSVANE UK Design 300b. The NU 45 ST shape from the 1950s have killer liquid midrange and are like $50 each.
Cant recall offhand which tubes are allowed in the Balanced.
If I were you, I would be more into the recti search that complements those Globes:
Metal base Phillips GZ34, Fat bottle GZ37, the Brimar 5Z4 (cheap), the Haltron/Zaerix/Fivre double Mica 5r4gy, the WW2 RCA upward pointing double D getter 5r4gy (only $88), WE vintage 274B, Cossor U52 and the Footscray STC/Brimar 5R4gy unobtanium tubes. Big proops are given to the (expensive) Takatsuki 274B as well.