I might have to help out a friend with a WP swap on his Beemer so I'm in.
It's pretty simple really, if you want to keep the stock handling but with better quality suspension then just copy the stock total offset (triple clamps + fork lugs), fork length, and stroke.
KTM triples are available in a variety of offsets, although nothing below 11mm or above 35mm I believe. Fork bottoms on the WP43 and WP48 have the axle leading by 35mm if I remember correctly.
So what are those measurements on a stock G/S?