I've got myself 2 more bags of rivets and set off to add them to gearbox and floor. Took me 2 evenings to complete. I bet it takes a lot less time to do it on real car. I actually ran out of rivets again. So, I decided not to add all rivets to the floor. Added only those, which hold covers over exhausts and so prominently visible. Apparently I underestimated number of rivets needed. Well over 80 of them would have been required to finish the floor, gearbox and body completely.