From the centre of the stem to the centre of the fork tube top, if you look at the top clamp from a stocker it will be around 60mm yours will be around 20-25mm, my gsxr clamps are offset 25mm so i am having new clamps made up at 50mm, same as the 750 F.
If you draw a straight line across the top of both fork tops from centre to centre, then measure the distance from this line to the centre of the steering neck it will give you the offset, changing this measurement changes you trail numbers, which will alter the way the bike steers or turns in to a corner. There is a lot more to handling than just sticking any swingarm and forks on a bike.
Mick