Threaded headset help please?

I am currently refurbing a lovely Orange CR 16r and having to replace a few parts. The Original forks I want to keep along with the threaded headset, but the original is shot, as salt water has got in at some point, rest of the bike is virtually like new. I have now tried three different headsets, two Stronglight and a Shimano XT and none of the top races will screw down over the forks threads. The original spins down freely, the others bind after 1 and a half or so turns. The threads are not damaged, It feels as though the threads are a different pitch. Does anyone know if Orange dye'd their forks with a continental screw pitched thread? This is really winding me up and I do not want to resort to changing the forks to Ahead style or a headset converter.

I had a similar experience with a 1" titanium steerer - my Mavic headset would get jammed part way down. The headset would work perfectly with other 1" steerers and other headsets would work on the titanium steerer. But could I get the Mavic to work with the ti steerer? Could I hell! :roll:
Sorry to be of no help whatsoever but you have my sympathy.

Head in

Yes, they used to spec' Shimano STX and XT Groupset, so can't understand why it won't fit? I could get a dye and try reaming the threads again or buy another set of one inch rigid forks and Ahead them as you can get a top race converter for the XT headset. All this takes me back, why Orange still stuck with the one inch tube and threaded forks years after the ahead system came in beggers belief!!