A bike shop that has been around quite a while will probably have one or those reduction wild beasts <grin> that fits that old bike in one of their old parts bins. That's where I got mine when I built out my old Paramount with 11 speed stuff.

I've been thinking that the big hole on the bottom of your BB probably served both as a drain and something for the cable guide to snap into. I never had nice bikes like that BITD though. Mine where all the looks like a light weight racing bike, but in looks only.