Jerry, what sort of bolt are you recommending exactly? Can you share a picture or link?
The shoulder bolts I'm familiar with in the machine shop have Allen heads and the threads are one bolt size smaller than the precision ground shank size, 3/8" shank and 5/16-18 threads for example. I would not use these as frame bolts and have never seen them or an equivalent used in a frame.
I can sort of imagine a normal looking bolt with well defined shank length and diameter but don't know if they exist, we'll might be something special made special applications, but can they be found easily and are they affordable, is this what your describing?
My answer to the original question; put one grade 8 bolt in (as Mike said), its only missing one. Better answer would be flanged bolt and self locking flanged nut, as is/was commonly used on frames now or not long ago. Best answer is a new hot rivet set quickly with a pneumatic riveting hammer. Also best but unlikely to happen is cold rivet set with hydraulic squeeze riveter as the factory did.
Grigg
