I have a DJ-1 and did exactly what you are looking to do, well kinda at least. I replaced the non-steerable Pilot nose gear with a Robart mechanical nose gear. The dimensions are very close, but the Robart is a little bit taller and the retract sticks out the bottom of the fuse about 1/16". If you are really set on modifying the Pilot gear, do a search for "toki" by Easytiger. He posted pictures a couple of years ago on how he made his Pilot gear steerable.

John