Tony, that design would work very well, but unfortunately there are 2 mailboxes in close proximity to one another. The pivot would slam one into the other. I saw that design last year and it looked relatively easy to make too, but not with 2 side by side.
JKB, I must have misread the specs. If a shear plate style will work, that is good enough for me.
I could also camo it by taking 1x6's and screwing 4 together to make it look like a wood post.....
and NO, I don't think a RR tie would be any better but it might have made it more legal if the metal post wasn't allowed.