It's Alive!
The wider crank is supposed to be included; the 4-stroke kits I see online have it.
Two of the three pieces of a three-piece crank were included; I'm guessing the assumption was that it'd be installed on a bike that already had a three-piece crank. Mine, though, has a one-piece crank. I've found a couple of online sources for the parts to convert from a one-piece to a three-piece, but I'm going to check one of the local bike shops this afternoon to see if they have them on hand.
The replacement twist-grip throttle arrived yesterday. The grip area is rubber instead of metalized plastic, which I think will offer a better grip, and it doesn't look as "blingy." The cable from the killswitch was too short and missing the connectors on the engine end, but it was a few minutes' work with a knife and a soldering iron to swap cables around.
When I first hooked up the throttle cable, it wouldn't let the throttle close. I ended up fixing that by screwing the right-angle piece further into the twist-grip body...was a bit worried that I'd crack the plastic and need yet another one, but once it was put together, the throttle moved over its full range without binding.
The engine shipped with oil in the crankcase. Not knowing of its provenance, I dumped it out and put in a half-pint of Quaker State 10W30. Whatever oil you prefer to use in your cars, I'd recommend replacing what comes with the engine (but don't use synthetic oil for your first few fills, or the rings won't seat properly). There was a visible difference between the "Happy Time" oil and the Quaker State. The former was more pale in appearance; it looked almost like power-steering fluid, or the oil used in air compressors.
The fuel shutoff valve has a 1/4" hose barb on it, but the carburetor fuel inlet has a 3/16" hose barb. A couple or three dollars at Lowe's/Home Depot/whatever will get you the pieces you need to neck down the fuel tubing.
With the engine and fuel tank mounted to the frame, the twist-grip throttle on the handlebar, and the muffler bolted on, I fired up the engine. It took a few pulls the first time and made a bit of smoke as the oil in the top end burned off, but it idled smoothly and quietly. It makes a bit more noise (especially from the gearbox, it would seem) when you gun it, but at least it runs.
The chain needed a few links taken out. Others have described grinding off the exposed end of the pin, but there's a better way. The same tool you use to work on bicycle chains can be made to work with the heavier engine chain. The pin lines up properly, but the chain tended to ride up out of the tool when I started pressing the pin out, so I held the chain in place with channel locks and pressed the pin most of the way out. The tool won't press it all the way as the engine chain is wider than a bike chain, but you can grip the chain with the channel locks and the pin with slip-joint pliers and pull them apart to finish the job.
I then installed the chain, the chain tensioner, and some lights, and put some more gas in the tank. Las Vegas was getting dumped on pretty hard (it's monsoon season), but by the time I had put up my tools and picked up the trash, it had mostly stopped. Even though I can't pedal it in its current state if something were to happen with the engine, I took it for a ride...first a quick one through the parking lot, then a longer (~12.5 km...speedometer is set to metric because I could, and the bigger numbers are more impressive

) one around the neighborhood.
The chain tensioner needs to be adjusted to take out more of the slack, but overall it ran pretty well. Top speed on level ground with me (who could stand to lose a bit of weight) on it is around 40 km/h. Climbing freeway overpasses (I wasn't on the freeway, but there are frontage roads around here that run parallel to it), it slowed down a bit to 35 km/h. I think 30 would be a good cruising speed for this rig; it climbed an overpass at 30 without needing any extra throttle. In any case, it's faster than I'd get that bike going on nearly anything but a downhill run.
The fuel tank also tilted sideways while I was out, but that's just a matter of tightening the bolts a bit more (and maybe putting a rubber strip between it and the frame. Going over all of the bolts that hold everything together probably wouldn't be a bad idea either.
No more pictures yet as it's a bit dirty from road spray. In addition to the three-piece crank conversion, I need to get some fenders for it. Turn signals and a horn would also be a Good Thing. I'm thinking I can make LED-based turn signals that would also include the taillight without much difficulty. (LED headlights would also be cool, but properly integrating those would pose some packaging difficulty to get the light thrown down the road properly...maybe some of
these could be adapted to work.) More pictures should be available in the near future.