The seller MAY have taken them off of a 525, but they never came on a 525 stock. The 525 only came with WP inverted forks, not conventional forks.
The mid to late 90s saw KTM using both Marzocchi Magnums and WP Extremes and they are similar in style in the last 50mm incarnations of both of those brands.
The lowest casting for the front axle will usually have a WP cast into it or an M that is fat and in a circle I believe on the Marzocchis.
I am not an expert on the conventional forks so please verify what you can. I hope this at least gives you a direction to start in though.
it is easier to ask for forgiveness than permission