Torque Tube Coupler Rivet questions

[19Fordy]

I would like to install the special oil tube seal that prevents banjo gear oil from running down inside the toque tube on a "raked" 40. It's the red "gizmo" below.

To install it, the lip of the seal has to ride at point "C" on the coupler. The instructions say to remove the coupler rivets and drive shaft to do this so as not to damage lip of seal.

Rather than do that I would like to file down the head or heads of the rivets flush with the coupler so I can then easily slide the red seal over the rivets.

Are the heads of the rivets countersunk so that I could file them flush and not compromise the holding power of the coupler? If needed, I could MIG weld a new head on the rivets. I think those rivets are swedged in place. One of my rivets sticks out about 3/32 in. and looks like it was not completely pounded down to form a head back in 1940. Thank you for your help.