Awesome photo selection Ludwig and I agree on the unitized engine/trans approach to building a trike/truck. I just posted a reply to an inquiry on the Simplex servi-cycle site about the possibility of using a Honda style cg engine with 4 speed/reverse on a proposed trike build. I'd assumed he intended to base this on the very beautiful Simplex truck frame, but now I'm not certain.
I also suggested the idea of adding a go cart style cvt with reverse box; cable and 3 position- forward, neutral & reverse hand lever. These are readily available, reasonable quality units capable of handling 13 hp with the 30 series cvt. These are 3/4" - 3/16" keyed output shaft ready and cost about $120., not including the cost of the cvt. & accommodate a variety of common chain and sprocket sets Either way seems a winner.
The other truck option is the use of the 3 D clutch coupled to the go cart reverse gearbox on a Predator or Honda engine. 212cc torque for the workhorse truck...single speed is not necessarily a problem with a work truck., but the addition of reverse makes these fun trikes and trucks real game winners.
While I have projects enough to keep me occupied I often think about the real world possibilities of using what already exists to improve what we already like. I'm just promoting the possibilities.
Rick C.