According to the thicknesses mentioned on Sheldon Browns website, for a cheap wrench 0.28" and a cone wrench 0.08" the difference is 0.2 inches, which I ground into dust. In a search it seems there everywhere, but in local stores.
The turn buckle I will add more length to one side of the threaded 3/8 rod with the hook. I have a low profile coupler nut with two extra nuts and lock washers to attach it. This will make it clear obstructions and I will not have to temporarily remove the banana seat bars at the drop outs.
Dumb luck I took the right hand threaded side of the coupler which is what I wanted. I have to still put finishing touches on the tensioner.
FYI, I was in a OSH store recently and all the bags of a particular size of left hand nuts were actually just right hand nuts. The store help was going to leave them there even after he tried them also. I for the Heeel of it just brought them to the manager on the way out.