Well I have one of Will's amps as well...
Looking at your picture, the 2 white jacks in front of the power transformer(big one in the middle) are where you will place the red lead of your meter to measure the bias. The black lead of the meter, you will place somewhere on the amp chassis for ground.
Next to each of the white jacks, you will see a slotted knob. Those are what you turn to adjust the bias.(Turning left lowers the bias, turning right raises bias)
To start, I would turn each one a very little to the left to lower the bias some.
Turn the amp on and let it sit for about 10-15 mins to warm up some.
After the 15 mins, check the bias voltage(make sure your meter is set to DC voltage) and adjust it accordingly.
IMO, for that amp, 1.45-1.5v is good.
The left jack and knob are for the left power tubes and the right jack and knob are for the right power tubes.
Make sure to have speakers plugged into the amp but do not have anything playing at the time of adjustment.
Just an FIY and IMHO....I find that the EH 6ca7 Fat boys work and sound GREAT in that amp!!
Hope this helps you out!