I have a 1954 NAA with the usual non-live PTO. I need to replace the clutch, I assume it has a 9 inch clutch as standard from the factory. Is this assumption correct?

I would like to add to my previous message concerning the size of the clutch in my 1954 NAA. Does the clutch disc have a 1-3/8 inch ten spline center?

You are correct.
As an added bonus, if you have a future desire to not have to block the clutch open due to the new environmental standards and the reduction of zinc and copper in the new disc, you can locate yourself a Kevlar disc. However Kevlar does not tolerate oil leaks or slippage. Kevlar though will not freeze in place due to a lack of materials.