Hi Rennie, I believe that the hardware is rather easy to find/make. The threaded tensor you can find it in any hardware store or ironmonger, remove the hook and the loop and use the central part. Then make the long parts out of an iron bar, with a 1/2" long thread at each end. Then fix one of those threaded loops (see image) on each side of it.
I personally do not like the way this guy has attached the tensor bar to the leg stretcher, it makes it look too farfetched to me even if the original was like that.
I would use an open loop hook screwed onto the stretcher and after puting the loop in close it.
You can use a chain instead of a bar, or make an striking contrast using a polished stainless steel rod, try to find suitable parts at carwrecks or shipyards that do not necessarily need to be or resemble like the original ones, feel free to change those things to your liking, be flexible enough to accept that.
As per the wood choice, why not use salvaged rail sleepers? they are hard, and treated with creosota, so wear a mask when working them if you use those.