John, Yup, it's a "Z"!! There is absolutely no doubt. One gets use to looking at these little devils and it gets easier!! Trust me. The only ones that are tough for me are the "g" and "q".
Your magazine should be an SE/655 acceptance mark!
The original issue magazine should have been stamped with the serial number and a "Z", an SE/655 and a N3894. Without the N3894 stamp, the magazine would only be an approximation!!
Hope you get Lucky!!
