Funny thing, my 1959 3100 had the exact thing- all shock mount studs were smooth.....no threads to secure the shocks. I don't think they were broken off either- the ends look designed that way...
ChuckC, I recently replaced the original shocks on my '59 and encountered the same thing. That must have been how the original ones were designed. While I'm more comfortable with the new hardware, which has nuts, the original's without nuts held the shocks just fine for almost 57 years.
Bob
