Hmm. What size tires do you have? Are they overly large? How about looking from the rear, with the engine over as far as it will go, will the chain clear the tire if the sprocket was lined up correctly? I mean, if you got the sprocket to line up, will it still clear the tire by 1/2 inch or so.
The best way to move the sprocket in is to turn it around. If you had another set of rubber moons, you could turn it around and use 2 sets on the outside of the spokes to bump it out a 1/4 inch, like some people do with the wide-tired stingrays.
Edit: I haven't ever seen the 4stroke kit in person. Are you thinking that you could elongate the mounting holes and slide the motor to the left? **edit** I see that you are. ** That seems doable. I wouldn't think the balance would be that far off but the mounting may be less secure.
Also, I think that you can buy non-offset sprockets that would let you half the distance that you move the teeth by flipping