Very impressed in your fabrication.
That must have taken some time to work this out.
I looked at a similar arrangement but because of the two drives I was pushed for space.
So I compromised by diverting the jet under the boat. To be honest they are hardly used.
I will get back to you on the boat dimensions.
The design was a model boat mag, however it used props rather than jets.
The boat performs well,
I had a few problems with leaks around the drive, also had a problem with one drive , internal prop moved within the assembly resulting in loss of power.
You also have to ensure you ballast the boat to ensure the jet are under water or they will air lock.
The motors do heat up, so running time is limited.
I found out later that the motors can be water cooled using the water jet that comes out of the top of the jet.
I am not sure of the purpose of this jet maybe somebody in the group can enlighten us.
I note jet skis have this jet as well.
The jet units themselves are quite flimsy
and in my opinion not very well designed for fitting in the stern of a boat.