I'm no expert but feel confident I'm right. Yes they can be swapped over. There were 3 cams made for the twins. The first up until 59 when the G12 appeared, post 59 for the G12 and the last is the rare race kit cam. The CSR models used the same cam as the others but had higher compression. Compared to each other earlier and later cams look similar but timings are different. Hope this helps Greg
You dont say what year the G9 is but the later cams from 1953 onwards will fit in the pre 53 motors but you will have to check that on full lift the valve springs have at least 1/32 clearance and are not coilbound. I have just completed a rebuild of my 52 model 20 and fitted the later cams into the motor.