I'm seriously considering making up a chainring from some of these templates and running something like 64t/23t, assuming I can fit it with the chainstay (though its an old frame, I wouldn't mind 'modifying' the chainstay if necessary.

http://www.ihpva.org/Builders/Sprocket/

If I could find track cogs bigger than 23t, I'll do even more. Supposedly cassette cogs come in up to 34, but I haven't seen them yet... a 92t/34t would look crazy.

peace,
sam