Great Pics dirtdevil. I'd say he has a 3/32" chain, considering it came from a geared bike in the early 90's, and not a BMX or track bike.
Also, don't rule out a Surly cog! They just started selling their cassette cogs, and they look beefy as hell. For a comparison I nabbed this from Harris cycler. From left to right: Shimano BMX , Chris King, Shimano Hyperglide (AVOID), and Surly.