Nothing here you probably don't know, but this is what I have learned from my TTen project:
2 cylinder minimum. If you are on fresh water, you can get by without a freshwater exchanger, original equipment. If you do need one, because might use it in a saltwater area, you'll need to raise the engine cover to clear the riser on the heat exchanger.
When you start to get into this, a lot of other things will come up. The biggest will be a saturated core under the engine pan. Look closely, and check with a moisture meter from below. This hull area has very thin glass and is prone to problems from engine vibration. The last thing you want to do is drop in a new engine only to find you have to pull it to repair the area. However, these repairs have been made from the outside. Hope that's helpful.