I have a 115hp yamaha on a 20'6" alumacraft prop tunnel hull with the sponsons. I have a hydraulic jack plate, 6" I think would have to check on that.

If I wanted to put a jet lower on would it work as is? I am familiar with power reduction.

If it would not work, what is needed to convert this to a set up that would work with a jet if that is even economicAly feasible or possible.

I would like to be able to go back and forth between the two of them. I can handle moderate mechanical work, but not fabrication. I fish trinity river warm months for fun and guided, lake palestine in the winter fun only.

I run a jet. What you've got will work but it's not really optimum.
Tunnel built for a prop is too big for a jet. Best is only 1-2" high and just wide enough for the jet foot to fit in.
Setback kills a jet, you want the intake as close to the water flow as possible.
And you'll need to raise your motor about five inches to get the jet intake to the top of the tunnel.

You can make it work semi ok with the jack plate and cavitation wings from outboard jet but it's going to really suffer if you get in rough water with that big tunnel.