I found this package of 10 M8 x 1.25 x 62mm studs and 10 nuts pre-packaged at NAPA. Looks to be an exhaust manifold stud kit?? Studs are plated (so they won't rust) with a small hex swaged on one end. Nuts are deformed thread locking type. Studs are the perfect length for mounting the bumper with dog bones to the car, front and rear. Thread the stud through the bumper bracket with just enough thread on the backside to lock the nut and retain the stud. The remaining stud sticking out is the perfect length. You'll need 4 additional nuts and washers to complete the bumper install. Number on the package is 600-2604.
Andys