You can use a long shaft on your boat look at the picture of my red boat
That is a 2x12 with plywood bolted to the boat to bring the prop as high as it can go and still work..
If you build one make it higher than needed try it, keep sawing 1/2' off the top till you get full speed, I found I had my motor running 6" shallower than normal with full cooling working... and seemed I was hitting bottom a lot less, also do not forget to tie off your lock down so if you hit the unit will swing up...
I could not afford a jet for years, and a prop worked for me.. just make sure you have a spare prop and tools... just in case