I seem to recall I just used long 6mm bolts and washers to fit a different seat, I think the bie was my k3 and the seat was a 500, but it was 10 years ago, and the bike was a complete shed, built up out of a load of scrap on a tiny budgett, it did look quite smart with a set of comstars and twin disks with braided stainless lines and bolts - I think the front brakes cost more then the rest of the bike! It's still here too, but dismantled into the loft for storage and rust prevntion.