For a 6L6, the load should usually between 4k and 5k. so the same connections as the 6v6 should be fine. An EL34 is different, its load is a bit less. so for EL34’s you would want the tube connected to either the 2.5k, or the 3k taps and on the secondary and just attach your 8 ohm speaker to the 8 ohm load. to make it easy to switch between all of them, connect the primary to the 2.5k, and on the secondary you can put a switch to change the secondaries from 4 to 8 ohm. This way you will be able to switch the primary impedance between 2.5k and 5k depending on what tube you decide to use.