If you switch the stock PAS to full blend for mono operation, the inputs to the two-channel linestage are connected together. There is no harm in doing this, but without those 47K resistors in the signal path, you'd also be connecting the outputs of the phono stage together, blending the separate channels' negative feedback in the phono stage. Feedback should be kept separate for each channel (and that's one big reason why paralleling the two channels of the Stereo 70 to get a 70-watt mono amp really doesn't work). If you choose to eliminate the blend switch there should be no harm in eliminating the 47K resistor. I play mono records frequently, and listen to FM in a fringe area where switching to mono reduces the background noise, and have chosen to retain the blend switch; so I have to retain the 47K resistors.