William,
The forks were a gift off a fork-lift truck.
I had already drawn plans and checked on material to use 2x4 channel iron for the forks and the hollow 2x4 you see at the top of my forks for the vertical.
My welder was going to cut 3x1.5 solid steel and bend to 90 degrees for reinforcement at the bottom angles.
The weight would have been less than the 100 # each that I have but the strength would not have been as great.
However; I don't think the weaker option would have been a problem.
Just guessing about that.
One more thing to consider, the angle of the forks when on the bucket.
When I load my forks with brush and get to the dump pile the full down tilt does not let the brush slide off without some shaking. If the angle was a little more than the 90 degree then the forks would drop at a steeper angle when the bucket is a full height. Huh? Did I make that clear as mud?
Also note I can put 2x4 wooden stakes into the top of my forks to keep light weight loads from rolling back.
Hope this helps, if you have more questions ... holler.
Norris