Nice link, Ross. It appears the end boards have a rabbet of 1/16 inch on the ends, I only measured a couple of center boards. Hopefully the original poster checks back as the width of the rabbets is different too.
When these trucks were built "as trucks" the steel ribs were designed to be higher than the bed wood, thus saving on damage and gouging of the wood.
However, it gives the bed a cleaner look when the bed strips are flushed into the bed wood, a rabbit of 1/16 inch will have the strips raised above the level of the wood, even a 1/8 inch rabbit will make them a bit high.
I suggest measureing the deck height of your bed strips (my original's are 3/16 tall) and make your rabbit suit the look that you want. When I cut the boards for Jon's 50, the stainless ribs were 1/4 inch high so thats what I made the rabbits because he wanted everything flush and smooth.
This is kind of a PS; I bought the clear grain white oak boards for Jon's truck at lumber liquidators for less than half what the supply houses want for bed boards, You just have to do your own saw work.