It would be helpful for us if you posted that schematic so we too could see the circuit.
Converting any amp from 6L6 (presumably) to EL34 includes the following considerations:
1. EL34 needs 1.5A for heater instead of 0.9A. SO a pair needs 1.2A more heater current from the power transformer. SO is your transformer able to do that?
2. The EL34 does not have internal suppressor to cathode link, suppressor is on pin 1, which needs to be linked to pin 8. Are your sockets on a pc board or hard wired? If they used pin 1 as a tie point - as is often done in 6L6 amps - that will have to be rewired.
3. Screen grid resistors would want to be 1K 5w, the 6L6 probably has smaller resistors there.
4. The EL34 probably wants lower bias voltage. If the 6L6s are running at -55v say, the EL34s will want more like -42v. SO your bias needs to be adjustable with range to cover that need.
Cover those things before worrying further.