cab differences...help please

[bigblock73]

As you may know...I designed and sell cab corner speaker brackets for the 47-54 trucks. I used two different cabs for mock up, but both were the standard cab models without the corner windows. I have a customer with a 47 that has the corner windows...and he has sheetmetal in the rear cab corners...whereas the 48 and 52 cabs I used were open. Is this gentlemans 47 original (minus the suicide door setup of course), and if so, is this a difference between the two cab differences (window configuration)? I want to make sure I am taking care of the customer, and want to respond with factual information. Thanks in advance for your help everyone.