Or you could just do like I did.. head on the floorboard, back on the seat bottom, **** on the seat back and legs tucked over the headrest. Don't have the luxury of one of those little boards when doing under dash stuff trapped in the air on a symmetrical lift
It's impossible to tell from the photo's as to whether there's any extra bracing underneath, but regarding the grain, that's pretty much irrelevant. Ply layers have the grain running 90 degrees to the previous layer.