It's a 34. I think smaller would be better for my needs but this is what I had.
I laid out a circle the size of the cog on a piece of wood with a compass. I set the cog in place and locked it down with a couple of wood screws between the teeth. I got the BCD off Sheldon's site and drew a circle on the cog of that diameter, using the center that I'd drawn on the wood. Then using that diameter and the compass, I divided the circumference into 6 and punched a dimple on 3 of those marks. Then I drilled a little pilot hole and followed it with a big bit the size I wanted. I should have waited till I could go use the drill press at the shop but I got anxious and just used a hand drill.
I replaced the whole thing a month or two ago with an alloy cotterless setup just cause I finally found a spindle that works with this bottom bracket but I might go back, just cause this bike looks better with chrome and I think most of the troubles I was having were more to do with a worn derailler and chain. I can't believe I've put enough miles on this bike to wear out a chain already.