According to the FAM, on a 3100 just the front running board brackets are left and right specific. It shows only a single PN for each of the center and rear brackets with no L and R specific number.
Section 2, Sheets 7.00, 7.01, and 702 are the pages that show the numbers.

Last edited by klhansen; 03/07/2020 5:08 AM.
Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.