Re: Boat set up
Go up an inch by moving the bottom bolts to the lower hole, then get a 13 X 19 prop. 5600 is 100 over the operating range. It will not hurt anything but a 19 pitch will drop you to about 5200 which is closer to the middle of the 4500-5500 range. loosen the top clamps, remove the bottom bolts and use a pry bar under the mounting clamps. Temporarily put in wood blocks to hold the engine up then re-bolt the bottom and tighten the top. There is no need to fill the 1 inch gap above the transom. Whole job should take 15 min to 1/2 hour.
With that slight flat riding pad at the bottom of the transom, you may experience some ventilation/cavitation but a cupped prop will help. Also, try to find the black plastic "Flare Washer" that fits on the prop under the nut. It is about 4 inches in diameter and an inch thick, tapered. It helps with the hole shot. However, you may find as I did that you still will be able to use full out/up trim.
I have my 90 on a 15 foot Glastron and she gets 43 MPH GPS at about 5200 RPM with a 13 X 19 stainless prop. She is jacked an inch and I do not get any cavitation on the hole shot or during cruising. I do ventilate a bit in relatively sharp turns--that is, turning in a 500 foot wide river. As a matter of fact, my Glastron does not like any in/down trim and becomes very squirrely. She even likes to do the hole shot with full up trim.