Think of 2 inch as a "class" of speaker, not an exact dimension. The unit is not too wide for a P&D F3 body shell. The front porthole window glass inserts may need modification if the speaker is attached to the frame. Sound exits the car body through dynamic brake screens on the top and car body air intakes on the sides. Some P&D F-unit shells have molded filters on the sides, but those can be removed with a little care.
Unfortunately the speaker is definitely too tall, so a hole needs to be milled through the brass frame to accommodate the passive driver that extends bass response by about an octave.
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Note that the HO decoder is just for acoustic testing. The 8414 Pittman motor has a stall current of about 10 Amps so a V4L will be used.
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Some of the front motor mount and bits of the plastic I-beams under the frame must also be trimmed. The speaker will probably be glued to the frame with silicone caulk.
The cab insert shown does not come with the P&D kit. It is part of a very nice cab detail kit available separately. Here is one I built in 2004.
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All the best.