First off, awesome to see another morgan-style reverse trike in the works.
Martin, forget reverse or any kind of mechanical reverser. I push the B-3 around all the time. it only weighs 910 lbs, so its easy to push, cake in fact, and I like cake. This past weekend I ran it out of gas (oooops) and had to push it about 1/4 mile to the nearest gas station, and it was easy. at one point I was just walking along beside it lightly pushing on the steering wheel and steering at the same time. I often tell people that the reason I put the roll bar on it was so it'd be easy to push, and it is. design in some push handles/pads, and you'll be fine.
also, adding a reverser is extra weight, so... the B-3 will never have one. pushing is part of the experience. its not a car.
the modern Morgan three wheeler has a miata transmission attached to an S&S X-wedge V-twin via a rather complicated driveline isolator mechanism. you won't have that. from my own experience on the B-3, I'm going to add a guibo style driveline isolator on the next one. the B-3 clanks a bit on shifts, and you can sometimes - very seldom actually, it has good flywheel effect - get a bit of driveline jerking on and off throttle, but its not bad enough to make me want to change anything.
your driveshaft will be offset to the passenger side, and you're going to need a multiple piece driveshaft to get from the engine to the swingarm. the driveshaft in the B-3 is two piece, (not counting the section that's actually inside the motorcycle swingarm, B-3 has a Suzuki VS1400 swingarm) you'll need at least that, and because of the driveshaft offset, the driveshaft will have to pass partially underneath the passenger seat, which will limit how low you can mount the seat. you're going to need to support the rear section of the driveshaft (which goes under the seat) in a pair of bearings so that it can support the driveshaft section within the swingarm, since that would otherwise be supported by the output shaft on the GL engine. I used 1.0 ID race kart axle bearings, and they're holding up fine.
in the B-3 the driveshaft is within 1.125 inch of the bottom of the drivers seat with a 6061 aluminum cover in between.
when I do the next one (the Martian Buzz Bomb, powered by a Suzuki GSX1100G four banger - the shaft drive version of the air-and-oil-cooled GSXR 1100) I'm going to use 1.25 ID race kart axle bearings because for those you can get bearing mounts that are self aligning.
I have had the thought that it might not be absolutely necessary to have the under-seat driveshaft section present its end to the swingarm driveshaft section directly horizontally, but could be angled a bit which would have allowed me to mount the seats lower - if you can visualize what I'm talking about.
both the front and rear sections of the B-3 driveshaft are made from 1.0 inch OD .188 wall DOM with motorcycle spline ends (a combination of Suzuki VS800/1400 series and Yamaha XS750/850/1100 spline ends cut from the stock motorcycle driveshafts (Ebay), machined for a tight slip fit into the DOM and welded. 8600 miles, including a dozen-or-more fat smoky burnouts and everything is fine.
you're going to need to support the rear section of the driveshaft in a pair of bearings so that it can support the driveshaft section within the swingarm, since that would otherwise be supported by the output shaft on the GL engine.
Having built the B-3 and happily winding up with a pretty much successful and solid daily driver, I've learned a bunch of other lessons, feel free to ask anything, I also have a huge archive of pictures and video - waaayyy more than I showed in my build thread. I'll be happy to describe any of my design solutions should you be curious.
you should now be on ebay collecting GL1100 universal joints and driveshafts
_________________
The B-3 build log:
http://www.locostusa.com/forums/viewtopic.php?f=36&t=13941 unfortunately, all the pictures were lost in the massive server crash
The beginnings of the Jag Special,
https://www.locostusa.com/forums/viewtopic.php?f=36&t=19012Again, all pictures were lost.