I'm a big centurian fan, so I vote for the dave scott. You could always locktite a cog and bottom bracket ring on, stick with the inner chainwheel as Robbietunes suggests and have the thing running for $35 without selling any old parts.

BTW i rode fixed gear before it was cool and I'll probably ride fixed gear after its cool. It still is the most reliable and safest bike to run in a Minnesota winter.
OTOH, for dead reliable transportation bikes, I'll probably just ride the parts off whatever I'm riding and singlespeed the thing out.

Current commuter and all-rounder is an '86 Centurion Elite RS with the original crankset and front derailleur, Campy Veloce 9-speed shifters, ultegra 8 speed rear d, SRAM 9 speed cluster and a shiftmate to make it work. Brakes are Campy veloce from just before skeleton brakes. Saddle is 70's Wrights. Bars and stem are very pretty 70's japanese pieces. The best of the 70's 80's 90's and 00's