Thanks for digging up my old thread.
The forks has seen a lot of use. The only improvements I made for them is to weld some gussets on the the fork part itself. I cracked one weld after using the forks to ram some railroad ties I needed to get out of the ground.
If I were to do it again I would probably go with slightly thinner steel for the backing plate and slightly thicker steel for the forks. They are a bit flexible as they are now.
You could also reduce the length to make them a bit less bendy. About 36" length in front of the backing plate should be plenty. Mine are approx. 44"
I will look through my old files and see what I can find. I seem to remember that I had an AutoCAD drawing for some of this.
There was another member that used them for building his own set although we made some modifications to make the fork with more adjustable.