You can go to the microfiche for the steering of a 2001-2004 B12 at Ron Ayers
(click here) and see that the header for this page of parts covers the GSF1200S K1 ('01) thru K4 ('04).
You can also check the naked version
(click here) and see that the naked GSF1200 K1 ('01) thru K3 ('03) uses the same lower triple clamp/steering stem as the "S" version. (P/N 51410-32F00 or 51410-32F10 - both of which Ron Ayers charges $293.96 for)
Do you have the damaged original? Anyway to get any dimensions off it?
Hole spacing and diameters should match the upper, so if they don't that should be proof enough right there.