I'll be getting the whole drive-train kit from Zero. I haven't decided yet for sure but at this point I'm planning on the 5.8 kw (2 batt modules) with the 400 amp controller and the 75.7 motor.
I built the two trikes each starting with a TW200 motorcycle and then using all of the front end components from the YFZ450, Yamaha ATV. Plus the sway-bar from the Yamaha Grizzly 660 quad. There has never been a kit for this and I definitely needed my machine shop tools (mill, lathe, shear, brake,etc.) Plus the services of an excellent TIG welding person and lots of chromoly steel tubing. The front end parts etc., cost in the neighborhood of $5K The first trike cost me about $12K and the second one about $10K to build (including the bikes). When I add the approx $7,500 for the Zero power-train to the second trike I'll be at about what I paid to buy my CanAm Spyder, when they first came out. But I'll bet I'll ride it more than the Spyder.
I'll attach a photo of both of my "Yamaha" trikes. The things that look like drum brakes on the front are not. They are adapters I designed and machined to adapt the TW200 motorcycle front wheels to the ATV hubs so I could use the stock hydraulic disk brakes from the YFZ450. I'm proud that both came out looking like they were factory built. That was the first comment a Yamaha dealer said when he saw them.
I doubt that Yamaha would ever produce a trike conversion kit because of the liability. They all got scared away by the rear-dual-wheel trikes commonly called ATC's and the numerous law suits. All trikes should be built with the dual wheels in front so that a tip-over can be stopped by quick deceleration or braking. The rear-wheel trikes just flip faster when you try to burn off speed. Also you can't run over your own foot if both wheels are in front.
Many of those law suits were about that.
Sorry I don't have an easy answer for you to build a trike from a 2 wheel motorcycle. But if you decide to go that route your have my many good wishes for success.
I hope this serves to answer all future questions about building the trike itself.
My focus here will be on the conversion to electric power. Trikester