A newbie question for someone who is learning...

My Original 75 has the standard rear Diopter and I am toying with changing the eye cup (?) to a modern one with an adjustable aperture and possibly optical correction such as the Gehmann 530. I have taken the measurements I can and I think its M9 or M9.5.... From the Gehmann site for new Diopters I think their new standard thread size is M9.5....

Can any one shed any light here (pardon the pun) and any recommendations . do's donts...Shooting a variety of 6 yard bell target, 10m and >35Yards Vintage comps...