I looked into changing my Johnson 6 LS to a SS, but the cost is a bit steep. You need to get the shorter shift rods, water pump tube, and driveshaft. If you are very mechanically inclined and have the time and money it can be done.
I concur with Dogface. Go with a plate with a 5 inch lift. I've got one I can sell you that I had custom made to my specs out of aluminum to convert my transom from a 15 inch to 20 inch in order to run a jet motor.