Unless the boat is designed for a outboard jet, the transom will have to be raised so its way more than just lifting and remounting if you don't have a jack plate.
The transom height is important. The important thing is that the jet foot needs to be at the right location in relation to the bottom of your boat. The concept is that the bottom of the foot is 1/4 of an inch below the bottom on the boat. So 20 and 30 hp jets work great with 20 to 21 inch transom heights. Larger hp motors require 25 or 27 in transom. If you jet foot is sitting much lower than bottom of boat you will loose performance due to drag. If it is too high the motor will have cavitation. Folks try to use power trim to help. It helps alot but if your setup is wrong you still loose performance because trim up to raise the motor your actually rotating it backwards and upwards.
Find someone who understands jet to buy one from. Many dealers don't understand but will sell you one. Find someone who wants to take you for a ride and walk you thru a jet.
Tunnels can be good and some can be bad due to cavitation, especially when turning. Many manufacturers make tunnel jets...in my experience many have tunnels to shallow. They are great going straight but in a turn the tunnel is not large enough to feed enough water to the engine. It is all dependent on your boat bottom, engine, weight distribution.
You can have too much motor....meaning jet have to be under power to operate. 1/4 throttle does not work with jets. 3/4 to full throttle is needed. Matching the boat and motor to the water is recommended. 100hp on narrow streams don't work well because you have to go faster to keep on plane but it's not safe to go that fast.
14 to 15 ft boats with 20 hp jets are good and get it done.
16 ft boats with 30 to 40 hp are Swiss army knives.
18 to 20 ft require 65 to 110hp motors. Good for bigger waters, and taking family. But don't work well on smaller streams.
