The issue I am running into with what I have found thus far:
1) The designs that are around work. However have fatal material flaws. No I can not explain. i am parroting the statements of a fabrication specialist. I keep sending images and once he says he will build it, I will bring in some nice folks that owe me favors and will work the project because they are nerds and love me.
2) Lots of solutions work.. for very light loads, they are not materially or engineering challenged, they just rely on various factors that lack scale. Despite dropping 70 pounds since diagnosis. I weigh in at 260 still (yes, I am huge, and no, wasn't very fat before. I spent my youth doing physical things and it stuck) add 260 pounds, to the hundred odd pounds of kit I am gonna have strapped to a standard bike and we are at mechanical failure for many designs.
3) I can afford to build this, I just however will not spend "decent used car money" There are folks producing a solution that I could use... but they well, most of them *start* at 15k. I just can't do that for something that was built for about 2. I get profit. Just don't try to make it all off the disabled and physically challenged (I will cut the commentary there, but just mentally back fill a half hour of cursing)
4) I can't wait for the industry to cough up a solution. I am fighting health and time. I am ok with where this road ends.. I just don't want to get there on a walker.
Given your stated body limitations, do you need to travel at speeds above 20km/hr in a turn? The one time it all goes wrong (due to some car driver - not your choice), will you lose the ability to ride (or walk) at all? And if so, would it be better to choose a solution that doesn't involve high-speed cornering to avoid being in jeopardy?
That might relieve you of the need to have a leaning trike, and increase your options. The Greenspeed Magnum XL is designed for large weights, and a static frame of your own design should be achievable for much larger weights. Static, meaning 'not leaning'.
As well, you need the brakes to slow this 500+ pound vehicle. Might it be true that these limitations lead to a choice to keep the envelope within the boundary requiring any leaning at high speed?
You may still travel fast in a straight line. In my Motorcycle Safety Foundation riding course, I was taught to do all my braking in a straight line before turning, and from that lowest speed accelerate into the turn.
I have some physical catastrophes looming over me if I push my body too far in several ways (as advised by competent medical authorities) so I am deliberately trading speed for carrying capacity in my own design (see signature). It's not as much fun, but it's more fun that being in a wheelchair.
My trike is designed to carry my camping gear or shopping, tow a trailer, and get me up any hill I need to go up in order to get home and out of the rain. As well, this means I fear no wind or hill, so I will keep riding and moving including adjusting the motor input so there need be no strain on my joints - I wish it were just a matter of strengthening my muscles, I could do that. But some of my joints won't permit the loads needed to strengthen my muscles - so I'm designing for long term movement, even when walking becomes difficult.
If that limitation is otherwise a good choice for you, you can eliminate the worry about a leaning trike which would greatly simplify your design requirements.