John.
It is not all that different.
The number one thing that N&W had that was different was the boxy thing on the roof at the cab.
You can see it here. That bump on the hood roof not far from the horn.
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The other more minor difference was grills and screens on hood doors.
N&W tended to use boxy pieces with louvers.
Pennsy used screens that were flat with the door.
Here is an interesting photo.
Both are T-6s on the A&M.
One came from N&W and the other came from Pennsy.
You can see the filters/screens are different, but not that big a deal.
And the Pennsy unit would not have that bump on the roof.
Differences are minor.
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So you could take the N&W shell and grind off the bump at the roof.
It is made of pewter, so it is soft.
You would just have to go slow so as not to damage anything.