Honda-SOHC

Hi all,
I'm gradually rebuilding my K2 and am confused by sprocket size and fitment.
The drive sprocket has 17 teeth and the rear sprocket 48. The drive sprocket isn't set on the shaft and is able to slide freely and only stopped by a "C" spring clip located in a groove near the outer end of the shaft. The end of the shaft is fitted with an adjustable oiler.
Having read the description in the Haynes manual, it states.
Early models had a 16 tooth drive with 45 tooth rear, this set up damaged the chain so should be replaced with a 12 tooth drive with 48 tooth rear. The picture also shows the drive sprocket having a plate and two bolts, presumably to lock the sprocket in place.
Am I correct in assuming that a new 12 tooth sprocket with plate and bolts will fit the output shaft and that the 12/48 ratio is correct?
Regards,
Wills.