My 86 came with a sea drive, looks like it would also be the same transom as an io, but a guesstimate on mine would be 2 1/2-3 inches.
Next time I go down to the boat I'll measure it up, and post back.
Thanks, I am thinking I am going to use 3 peices of 3/4 and then glass over. That should put me at the numbers you are saying.