94 factory roof rack

I purchased a factory roof rack for the FZJ80(4 corner posts) The mounting hardware(rivet kit) did not come with. I was able to get the M5 screws(p/n 00278-93011) and the rivet nut(p/n 00278-00931) but there must be another bolt, etc to actually drive the rivet into the roof. I am assuming the rivets can be mounted from the exterior only w/o going into the ceiling.
Anybody know the remaining toyota parts I will need to complete install.
thanks