Hello again, sorry if I am doing this wrong in submitting a new topic instead of responding to the old one.
I have followed through with the R1 to M4 stock conversion. The Pistol Grip Stock #81040 and Collapsible Stock #70085 are interchangeable with minor cuts. The Benelli MR1 Pistol Grip Stock #81349 may not need to be trimmed, as the piece that needs to be trimmed from the M4 is not there.
You will need to buy 3 position tube but I went with and prefer RXARMS 6 position tube. Shot