There are only a few guys that have built their own brackets here. Strick in one that has done very good work in this field. Most guys either choose the Hermco fiberglass bracket or if you dont mind aluminum the Armstrong bracket. You would want to build one with as much flotation as possible so build for a twin engine application but just go with one 30 shaft motor.
If I were going to build one I would do the monkey see monkey do approach and copy one of these two Pros brackets and build from their specks. I would go with a 30 setback and a 13 degree angle. I know by build your own bracket you would save $$ but for me some things are worth splurging on.
FellowShip
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Just for the Grins
Official 23 SF Antique Classic SeaCraft Owner