I don't like the idea of Allen shoulder bolts or "stripper bolts" for use on frames.
Most of them I've seen which might have a suitable shoulder size usually have a much reduced thread size.
For example a common 3/8" shoulder bolt only has 5/16-18 threads and the threads have a generous undercut at the shoulder.

Also taking a clue from truck manufacturers they use flange bolts or Huck bolts or rivets. I haven't seen a shoulder allen bolt used in frame construction.

Here's a catalog with pictures of various fasteners for truck repair. Flange bolts on page 24
http://www.duncanbolt.com/images/truck_trailer_fasteners.pdf

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-