"I bought the $185 single row "upgrade kit" from Pelican Parts"
You are not the first ,nor the last(?) victim of the problematic Pelican instructions.
You do have a choice with the IMSB and replacing a dual row with a single row may be unwise.
Before you go much further it may be prudent to ask for opinions on the dual to single row replacement. A better alternative would be(?) the RND roller.
Or a generic dual row bearing with the original parts you already have??
http://lnengineering.com/products/ims/single-row-rnd-roller-bearing-ims-retrofit-kit.html