If your '40 pickup bed is stock with a steel floor you might consider a "Showdeck" from Bruce Horkey in Minnesota. I have a stock steel-floored '34 but I wanted a REMOVEABLE wooden showdeck. Bruce Horkey supplied precisely crafted maple boards (my choice of wood) and all the hardware. The aluminum underframe rests on sponge rubber pads so there is no damage to the original painted steel floor. Of course, I brushed on 5 coats of spar varnish (also supplied by Horkey).