I like the torsion axles as well, but it sounds like you want to keep it simple. Here's one more.
https://www.etrailer.com/Trailer-Sus...SP-169275.html
It looks like the rest of the hardware, except for a u-bolt or two are ok. I would add to launch the boat if you have some place to dock will make job way easier if you had not considered it.
Looks like there are spacers missing on rear axle.