Regarding the running boards, you are probably referring to "wide running boards", which in 49 was option #389, for half ton pickups. They make the running boards widen at the rear end by the bed, making it easier for someone to stand, such as paper boys delivering papers from the bed of the truck. I have actually seen these boards, but only once.
As for rarest accessory, maybe the electric shaver? Or probably rarer is the spare tire lock for the older style spare carriers. Those came with every 1/2 and 3/4 ton truck, but are now even harder to find than the carriers themselves.
