Re: Narrower chain?
The HD single speed bicycle chain is even to narrow. The kit sprockets vary in width but are at least 5/32 wide. It is always possible to face off the sprockets to 1/8" wide, but it wouldn't be worth it for no more than you would actually gain in width.
I have often thought about #35 chain, but there again it wouldn't be worth the hassel of trying to find, and do the machine work that would be needed to adapt the sprockets.