Those white plastic 1/2" thick cutting boards might make a good one.

Can you go bigger on both sprockets? That would get the chain farther away from the swingarm while keeping the ratio that you have.

Another option would be a spring loaded chain tensioner like the dirt bikes with long travel suspensions used to have so that there isn't enough slack for the chain to make contact as easily.

I understand the concern about drilling the swingarm.  Liquid Nails Heavy Duty that puppy on there!  Find an old tire and cut cha out a right-sized piece and liquid nail it on there!

There's nothing wrong with the belt.  I still use it, but people use chains for gearing and aesthetics. Or maybe they just wanted to do a mod.  But the belt drive is fine if it's your thing.

Oh, so you're trolling, just like you were doing in the gearing thread.  haha

Well then, one could say, "What's wrong with two wheels?" or "My motorcycle works fine with two wheels."  

The most common solution for this type of problem is a chain slider made of soft but durable material like rubber or nylon. These sliders are designed to be mounted on the swing arm where the chain makes contact.

Thanks for the responses. Still looking into this -- I'll throw up some pictures once I get a good mock up going. Complicating matters, I did remove the belt guard mounts when I put the chain on, so I may not be able to use a prefabbed slider. I'm inclined to try epoxying something on there If I can get it neat, but I'm not sure about epoxy/liquid nails holding up to any friction from the chain hitting it --- I've seen liquid nails cause entire sections of wainscoting to fail in more than one bathroom.