I drilled and tapped mine no problem. Used a workmate to hold them firm. The 'drilling' was done by hand (masonry drill bit held in mole grips) - more of a reaming process really than drilling. Very little material has to be removed - I think some have managed to tap them without drilling at all, but I found it easier to ream them a bit first.
FZS 1000 Gen1 (2003)
Tiger 900 GT Pro (2020)
Tiger 900 GT Pro (2020)