How do I know if I have the 105 tranny on my MKIII black?

My serial number is 15073. Must be one of the very very early MKIII's because as I understand, the MKIII serials started at 15000. I'm trying to sell the amp and the guy who wants it most likely is taking interest in it because of that which is cool. How can I tell if I have the rare 105 tranny that the MKIIC's had?

There are numbers engraved on the end bell of the transformer, not easy to spot if you have a head. If a potential buyer wants to be sure, you probably have to take the amp out of the chassis and take pictures.
make sure you take pictures of both the Power transformer and the Output transformer, since it's very likely you will get questions about that one as well.

But at first sight, the PT looks big if it's a 105.

Looks like I do have a 105 tranny. Thanks.

ohhhh yeah..pretty sure thats the one