As you said, there's nothing mentioned about the tweak to V3 pin 8 on the schematic, but the builder's guide says this about it:
Optionally remove the 47n bypass cap on V3 pin 8. Removing the cap would reduce a fair bit of post-MV gain, as well as increase bass, but may not be to the liking of those folks who would want a Triwatt for its earlier breakup compared to a DR.Monkey Mart GameThe other tweaks are in the cathode circuits of V1 and V2. The voltages there are really low, about 1 or 2 volts. You can use capacitors rated for 50 volts or higher, just to give it a good safety margin. The 64uF, 100uF, and 150uF are electrolytics. The 47nF can be the same as C1.
What impact does removing the 47n bypass capacitor on V3 pin 8 have on the overall tone and gain structure of the amp, and how does it compare to the stock configuration in terms of breakup and bass response?