Here is a fun fact for you all about bumpers. The bumpers were stamped on the same press as the regular bumpers but they laid down two sheet of metal when stamped then they pulled out the inner sheet and that left them with a thinner bumper ( and lighter ) than a stock bumper.
Bumper bolts…I’ll look in the paperwork I have and see if there are two different part numbers for bumper bolts.
I have seen many times where someone will spec out a different bolt is needed in a build and many times the vender will have that bolt in stock because they use it on a different model or brand. For example the k member bolts on these cars are 1/2” longer than a stock bolt. The vender had them or made them for this project.