I think thats the WW2 version, The 70's version has straight solebars and a fishbelly girder behind.
I seem to remember people saying the Genesis warwell was fiddly as you had to form the floor from a single flat piece, not sure about the warflat, surely it can't be as bad, its a flat floor and straight sides for a start.
I scratchbuilt a warwell using appleby bogies and jacks, there was an article in Model Rail a few years back with a drawing, and another article on MOD trains in Rail Express with a couple of drawings I think, definately a warwell drawing and maybe a warflat.
I think there may even be a Plastruct I section that is about the right size for the warflat solebars, I think thats what I used for one of those.
Mike