KW's riser with the floor attached is most likely the MD Juan version, which is slightly flimsier than stock. I don't know if I could recommend using it or not, maybe the new ones are heavier than the one I got almost a decade ago. Classic's rear floor had issues too, if they can make a flat one instead of the twisted one I got a while back, it may be worth it. I do know there have been improvements at both places. The Classic floor is heavier than stock and strong as can be.
The cheapest way to do this would be to purchase or far a new riser, then use flat steel to make the floor. It is About 36 by 39.5 from memory with a 5/8 flange turned down around the edge for welding to the wheelhouses. There are hat channels underneath, not as tall as the ones under your front floor.
Speaking of hat channels, you may want to purchase some premade hat channel material from a place called Nor Am �body parts, and use them to fab up new ones, if they are close to the stock size. Otherwise buy new prefabbed ones. �If the one in your tranny tunnel is bad, Midwest military makes a good one and I think Classic now has one. It is too complicated to make your own.
If you have a sheet metal shop nearby with a press brake or a good tight leaf brake, you can often have hat channels made pretty inexpensively compared to purchasing from the jeep suppliers. Just have them make several lengths of the sizes you need and cut off what you need to install.
