This transmission mainshaft fits:

1970 & 1971 SL350K1 / SL350 K1 / SL 350 K1 Motosport

This genuine part has been discontinued and is no longer available from Honda 

If you rebuild or restore any type of vehicle you know how important it is to use genuine / original factory / or high quality aftermarket parts. A repair or restoration project is intended to return that motorcycle to as close to original as possible, all the way down to last nut, bolt, cotter pin, cable or transmission mainshaft.

If there's even a chance you'll need this/these replacement part(s) in the future you'd better get them NOW!. Keep this in mind,  replacement parts are always good to have. When you decide to sell your vintage or classic motorcycle, including a few extra replacement parts always sweetens the deal for both buyer and seller.