As a reference point, our Mistress with SSMV's on boxes and 16.75x32 4-blade merc cleavers was initially set up with the propshaft centerline about 4" below hull bottom. No trouble getting on plane, 4000 rpm brought it right up. At this X-dim, it was really so deep that it would not even throw a tail. I've since knocked 3" of spacers out, but have not tried it out yet. If you don't have the boxes, I'd add an inch or two. Four blade props you can probably run 1" to 2" higher than a 3-blade.

A III doesn't have nearly the skeg of a V, so that might be a factor too. Better to keep a little more drive in the water to keep it from swapping ends on you.

Bigger, heavier boat, I'd lean on the side of keeping them a little deeper too.

Bottom line, for your rig 4" below is probably the right number. If you have the hatch clearance, you could mount them an inch or two high, put spacers in if you need them.

thank you for the input. i'm thinking of locating some 1" spacers and shooting for 3" then add the spacers to get me to 4" if needed