Agreed that the chrome on the fork crown may be beyond salvation... I have a Windsor Carrera Sport from around the same time period and remember it as being a decent rider (I haven't had it built in ~4yrs and I'm sure a better wheelset will help its case). From my sample size of one my impression is that these were fairly well made - someone was at least paying attention to what they were doing. Miters seem decent from what I can tell sighting/feeling them through the BB shell and head tube, paint is good, chrome is good (the chrome sock on the NDS fork blade on my CS is gone - though that's more to do with previous owners). Mine has straight gauge Tange tubing, different lugs (chromed head lugs still), same dropouts, different geometry. Spreaking for the Carrera Sport, it's nothing special, but that and the fact that it rides well enough makes it a good candidate for lots of use in places you might not take a nicer bike. I believe the Competition was at the top of their line - the components on yours would support that. These bike were hecho'd en Mexico (the story goes that Merckx's hour record bike received Windsor decals just before his efforts in Mexico City).

What's the head badge look like on yours? Black 'W' with red shadowing and black outline?

Check for a Columbus/dove stamp on the fork steerer tube. Its absense may not mean much, but presence would lend credence to the tubing claim by the seller.