One consideration is the front axle construction. The one you've posted uses a solid front axle which has to be much larger than normal bicycle axles, as it is only supported on one side. The consequence is that you can't use standard bicycle hubs or wheels for the front wheels on it. However, if you look up the Husky/ Mercurio tricycles made in Mexico, they use a design where the front wheels can be standard bicycle wheels, as they are supported on either side.
On the Worksman models mentioned, they have a large knuckle/ swivel underneath that is not a normal bicycle part, and would also require some ingenuity.
The shaft coming back from the box to the bottom bracket needs to be very rigid, as this is what keeps the rider from tipping one way or the other- you will feel whatever flexibility is present in that piece.
Before you make one, make sure you have a good place to use it. Around here (Dallas area), it's no problem to use a bicycle on auto roads. But those tricycles force you to take a whole lane whether you want to or not, and wouldn't be too welcome on busier roads, although technically legal. I use mine on side roads and bike trails.
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