Just ran the sims via John Broskie's TubeCAD. No change is necessary for subbing a 12BH7 as the long tail phase splitter. The bias voltages remain unchanged in this arrangement.
But using a 6DJ8/6922 doesn't get the right voltages as the LTP, and it's lower max voltage rating is a problem. The bias is more suited for small signals as a voltage amplifier. Unfortunately, it doesn't have suitable gain for a simple sub in the diytube ST70 driver.