Unlike my collection of parts I bought , with my unfinished speedster, I hope you have all the special nuts and bolts and metal brackets and braces which go from the body to the chassis.
On the grilles up front, I could not figure out the size for the nuts. No nuts came with my front grilles, only metal chromed grills and some screw in studs. I put the screw in studs into the back of the grilles and spend a good part of today at hardware stores and auto parts stores and never found any nuts which fit. So, the closest ones were 3mm metric, but those did not work. I ended up buying the 3mm metric and used a size 3-40 SAE tap on the small nuts. Got them started on the grille studs and carefully tightened them. Most places only sell the 6-32 SAE nuts or one selection of 3mm nut.