Classic Hatch strut Brackets

The hatch strut brackets (on the body not the hatch) on my 89 3.5 are broken. I have ordered replacements but I'm unsure how they fix to the body. The fixings look a bit like pop rivets but due to the weight of the hatch they can't be unless they are steel rivets. Do I drill out the fixings to fit the new brackets and what fixings should I use to refit Thanks Steve

If they are fixed by rivets, drill out the old ones and refit with new rivets, steel if you want to. There's loads of rivets used around the rear hatch of my RRC. Get drilling!