DIY static outboard bracket

[peiserma]

I am purchasing a used 175 offshore merc with a 25" shaft. I have a 20" transom. Thinking of making my own bracket using 4 pieces of angle bracket.

Motor weighs about 400 lbs, i think (per NADA) Smokeonthewater recommened 3x4 angle, but should it be 3/8" or is 1/2" safer? I Like overkill. Stainless? Or is Aluminum better? How many bolts should I use to attach one angle to another? 2 or 3? And what size bolt? What grade bolts? How many bolts to attach the bracket to the transom? How many to bolt the motor to the bracket?

Any thoughts appreciated.