Here are mine, made 3. I did these before we had the DIY section so I didnt document! There aluminum!
I made one a few years ago but it didn't turn out them best. Now I just use a 34" ez hanger and a Muddy micro mount.
Made them from aluminum! There Tig welded! They adjust up and down and side to side! I just looked at pic of a third arm mount, got out the pencil and drew my own plans up, they work great! I have $.86 cents in each one for carriage bolts, already had the aluminum.
Not really finished just got done welding some things and did a test. it extends to about 3 feet for so.