bikepartsusa.com has some really cheap 27" wheels, and also a nice 700c track wheelset for $133. +1 on the brakes being adjustable for 700c wheels: I've tried this, it works.

I've got a "coffee" colored '77 Raleigh Grand Prix. According to catalogs on Sheldon Brown's site, the frame is 2030 steel, which seems to be a ho-hum material since I could not find anything interesting about it on google. Metallurgical snobbery aside, the frame rides smoothly enough, and feels pretty light for steel. The current 5-speed + friction setup works really well and it seems stupid to change it. I've been trying to wrestle myself into going through with the fixie conversion, but the freewheel-loving part of me just won't let me do it.

Looking at the cranks, if you can remove the unwanted chainring you can use the same crank and BB for the fixed setup (assuming the chainline isn't too bad). That leaves the chain ($10), wheelset (~$150), cog (~$20), and lockring ($10-20).

$200 to convert a perfectly usable 5-speed with a she-will-do looking frame into a fixed gear? It's a tough decision...