M1A Installing a homemade dummy selector

Hello all, I am having fun with my M1A you all helped me purchase a few months ago.

So now I decided to install a dummy selector on it , but of course I can't do it the simple way and simple buy a kit! So I have gathered a selector group to make one myself, but ran into a question with regards to some interference but would like to alter the group as little as possible.

Sorry if this is obvious but my assumption is when the M1A was redesigned from the M14 the geometry of the receiver on the right side was altered since the selector group was not needed. There is a square stud in the middle of the connector assembly arm that appears to be interfering with the receiver re seating into the stock. I assume I would need to grind it off to allow installation of the group into a M1A. The sear release is also interfering whit the receiver as well.

Has anyone else attempted this and am I correct I would need to modify these two parts? Thanks Ike