Not sure if a 47 would be the same, but on my 51 3100, I cut them 2" x 2" x 2-1/8" tall out of scrap pieces of treated 4" x 4" posts. Drilled a 1/2" hole through the center, put a couple coats of back paint on them, and used a piece of gin belt (which was about 3/16" thick) as the rubber spacer. Everything lined up and the bed sits correct.
