Yes, there should be a wood block under each cross sill that has a bed to frame bolt except the rear sill, which sits directly on the end of the frame.
I'm getting a 1951 3600 put back together
Also one of my center sills has brackets welded on the ends - is that from the factory? Does that sill go in a particular location?
That cross sill with the brackets is the second from front. You will see the extra holes in your bedside and angle strip where that bracket attaches.
Good luck with the project