Welcome to the world of chainsaw bikes.
I have moved on from the lever to a new reverse mount with a cable lift. It's all pretty much under
http://motorbicycling.com/f36/addition-ryobi-mount-info-3943.html
This is the latest mount information. Don't use that suicide throttle on the 42cc engine, it is too dangerous. Use a mountain bike shifter if you have one. Even a brake lever will work. You need to attach the cable sheath to the engine mount somehow so that it will move up and down with the engine. otherwise your cable will not work in both the up and down position.
Parts of the mount are all over. I have the craftsman 42cc engine which is a poulan. It is a fine engine.
Drive wheel, get yourself a steel bike axle peg about an inch in diameter. Make sure the axle hole will fit over the drive shaft and threads. If it won't drill it out so that it slips over them easily. The threads won't need to go too deep because you are going to have to get the butterfly nut from inside your clutch assembly welded it onto the peg. thats your drive wheel.
Mount: I use a piece of angle steel brace from the hardware store. Let it hang over a few inches on the ends. You can cut it off later to the size you want. Use the kind that those cheapo steel storage racks are made with.
I sit the engine on it and then I drilled a couple of holes in the bottom of the case. You won't be using the gas tank or the oil tank so it's okay to drill into the bottom of the case.. I run a couple of screws into the case. I cover them with some quick set epoxy to lock them into the case. Be careful once to put them in they won't becoming out.
These days I am using the chain tensioning rods from the chain link fence section of the hardware store to make custom braces. I run the braces from the angle steel at the bottom of the engine to whatever holes there are in the chainsaw case. I tie it all together double nut and locktite it once i am sure of the fit.
Hook it to the harp with a strap hinge. Use a spring for tension and a cable to lift it from the front.
This is the last incarnation of the friction mount. It is also the simplest and cleanest yet.
Ask any question you have. I will be happy to answer. I have pretty much moved my experimenting to my blog but I am working with that engine and a smaller poulan all the time so keep an eye there for more improvements to the design. You also need to read the two chainsaw bike builds I did here. Those posts are evolutionary so read them both to the end they aren't that long.
Friction Drive Bicycles