The BR29 kit that I fitted to my 500 K1 had following bearing sizes, Top 26x48.5x15, bottom 30x50x14.
To ensure you do not have a shortage of threads at the top you need to fit the right size bottom spacer, the one in your kit might be too thick. I did not use the top seal supplied in the kit.
Before fitting the bottom bearing to the steering stem just pop the inner bearing in place. The bearing will probably be flush at the bottom, mine was just slightly recessed, the seal made it just level.
I then fitted the smallest spacer I had under the bottom race if that makes sense.
PS I have a bearing removal tool that enables me to remove the bottom race without damage, a small spacer is needed to give my puller purchase.