OK----put 2 bplts--3/8 with sesctoion of untreaded shank into the two bolt holes---take a starret ruler ( 1/2 wide) put across the two bolt shanks, measure to top of port----measure to bottom of port---play with the constant values in this game ----3/8, .375, 1/2, .500, .1875, .6875, .875----a little addition, a little subtration, a little of this, that, etc----if you can't fiqure out the diminsions--------