The output transformers, while rated for 60 watts are more like 100 watt size. I'm getting 72 watts output at clipping with none (as far as I can see) any saturation at 20 Hz at full power.
Also unique is bias adjustments for all 4 output tubes. This required doubling the number of coupling capacitors, bias pots, and grid leak resistors and fitting them all on the tubesforhifi Octal driver board for the Mk III amps. It required a couple of small holes to be drilled; relatively easy. This way the bias can be precisely adjusted for each output tube. Notice the jacks for the meter probe were added topside adjacent to the output tube that is getting adjusted. I color-coded the bias pots to match the color of the bias jacks. The black colored jack is for meter negative probe.
A couple of other details. I redesigned the circuit to run a 6SL7 in the front tube position. I also changed the wiring on one of the boards so one channel always runs one section of the 6SL7 and the other channel runs the other. Originally as designed, one triode section of the 6SL7 is not used. This way, when the active section "wears out" simply swap with the other amp's 6SL7 and you will be using the previously "unused" section.