Using the swing arm from the full suspension bike solves many of the problem associated with three wheel conversion. While there remains some chance of the rear axle twisting from side-to-side much of that will be absorbed by the rear shock.
The question that then comes to mind is, where would you ride this? For me the natural habitat for the mountain bike is a skinny little trail through the woods. The mountain trike wouldn’t fit. Though I imagine that people in more rural areas would have a wider selection of dirt riding opportunities.
As I’ve mentioned before I have a special interest in three wheeler because I plan to continue riding into elderhood, but am always worried about looking like an old dork. The mountain trike is weird enough to be undorky.
With two days to go there is only one bid at $55. Well below the value of the parts and effort of assembly. (and as usual, it’s thousands of mile away from me.)