I want this lower mount bar to protrude out about 2" past the bed. This lower bar will need to be notched to accept the down tube. I got a $60 harbor freight notcher and it seems ok I guess. So I set the notcher to 20 degrees, rigged up my 1.75" hole saw and gave it a whirl-
Although it's a harbor freight notcher, it still beats using a grinder to try to notch tube. The notch will be rather rough at first but after you clean it up with a grinder and flapwheel it looks pretty good
Now I can weld these short lower tubes to the plates I cut and drilled earlier.
And finally bolt them to the frame-