904 Tail Shaft Seal Selection?

Hey guys,

I’ve got a 360 magnum and a 904 trans in my 1971 scamp. The tail shaft seal is leaking and I’m trying to source a replacement.

I’m seeing differing results and it appears there is more than one size seal.

How do I determine which seal is correct?

Thanks in advance
I would buy National ot Timken


https://www.rockauto.com/en/catalog...mission-automatic,extension+housing+seal,8624