I would be very surprised if a dead blow hammer wont get them going. One hand over the nut, holding the spanner in place and a few sharp taps with the hammer. Easy to forget that the off side is a left hand thread but sure you are well aware of that.

Doug
2011 Plus 4 in Rich Maroon

1972 750 “ComDom” sprinter
1958 Triton 650
1992 Triumph Trophy 900