I've just compared the fork from your picture, i agree the look very much the later type. I think the frame and fork are from two different complete bikes and been placed together sometime in the past, with components from an earlier bike being placed on the later year frame. I have a 2011 Tiagra groupset inc wheels that i plan to fit, after that at least it will be constant. should be an interesting ride once it's built.
You 'might' find that the 2011 Tiagra wheels are spaced to wide for this frame...
The chrome forks on my 1985 Competition are 531 as you can see from the picture.
The more I think about the more I come to the decision that based solely on the internal cable routing this is later than 1986. Guess it could be 1996, but nothing else points in that direction.
Is the paint original? The decals look like nothing I've ever seen before! The rear drop outs may reveal a little more about it, as W prefix frames tend to have Gipiemme ones at the very least, (well, they did in the 80's!)
Just wish I could find some more info on the frame I've just bought.. viewtopic.php?f=12&t=274341