I would have put a couple of 45 degree bends in that plate with some gussets added, or made the stiffener out of 1 1/2" square tubing instead of creating all the stress risers with the bolts and spacers. Of course, I'm accustomed to building frames that survive dirt track racing conditions, where the rule of thumb is "Build it three times a strong as you think it needs to be, and don't be too surprised when it breaks"!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!