Correction: 5.6k should read 5.6M.Does this also mean that I should tie the tail of the 5.6k grid leak at the input (V1a) to V1a's cathode, rather than to the "chassis ground point" where I have it shown now?
Going strictly by the book, I would say yes. For practicality, imo, no, because this should be a quiet, well filtered place in the amp.
Since the Reverberocket splits the B+ rail at the *B* node, it may be *theoretically correct* to have a second ground bus for the *D*,*E*,*F* nodes. To avoid a ground loop a resistor (most likely being bypassed with a capacitor) would be placed on one of the buses. I show the resistor circled in green below. I would appreciate @2L man to comment on this.
If I were modding the Reverberocket, I would probably add another filter node, creating some space between the first gain stage and the PI. I would place the additional filter cap near the first gain stage. I would run a single ground bus very much like you show it with the new node closest to the input/first gain stage and not bother with a second ground bus.
(chas, I notice the input section of your layout is different than the original. Not a bad thing just different.)