[Nasher]

I had the same issue with the same fastener in an Aluminium 900SS Swingarm.
Which you can't reach down inside of.

I ground the head off the screw so I could take the hugger off and get at it properly.

Then I tried just drilling out the remains of the screw and Rivnut, but even with a bit of pressure in the pillar drill the rivnut kept spinning round.

I drilled a 2mm hole down the side of the rivnut between it and swingarm using a milling bit which is obviously less flexible.
This should have given me half a hole in the rivnut and half in the swingarm, but of course the bit went more into the Ali than the steel, but there was enough of an arc cut in the rivnut that I could press in a mild steel pin to stop the rivnut turning whilst I drilled it out.

The ‘press in a mild steel pin’ sounds good, but in reality I hammered in a nail of the right diameter.

I’ve not replaced the Rivnut yet, but am convinced the Land rover ones I have are the same thread but a slightly bit bigger OD.

Nasher.