I would try lifting it by one hole, i have just rigged a Ribcraft 5.85 with a Mariner 115 four stroke, ended up lifting it by two holes.
Its great when the boat has a load in it but when its running light it cavitates alot in turns which is not so good.
I have set it up to be at Seawork next week were it will be taking people out for rides so its ok. When it gets back im going to put it down one hole.
Pete7 im suprised it didnt make a difference puting the engine in the center, but it does depend on boat size and what the hull shape is like. Deep V hulls like Seariders need lots of offset were as wider hulls dont need much off set.