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Noted that Bowser/Cal Scale has a GP-9 antenna supports part number.
#190-3050 GP-9 Brass wire is used for the antenna.
Quick internet search
According to Pennsy Diesels 1924-1968 by Douglas and Weiglin, there were 145 (road numbers 7000 to 7144) of the 310 GP-9's that were equipped with trainphone.
The book does not specifically discuss fan size, but it does contain this information:
1) The trainphone units were all in the first 3 orders (of 7 total orders) to EMD, ordered May 1955 to November 1956 and delivered October 1955 to June 1957.
2) Non-trainphone units were ordered April 1957 to November 1957 and were delivered November 1957 to December 1959.
3) A roof photo of unit number 7098 (part of the 3rd and last order for trainphone units) on page 219 of the book shows trainphone antennas and a pair of 36" fans.
My guess would be that all of the trainphone units had 36" fans.
I don't think any GP9s came with 48" fans. That was something that was started with the GP18/20s.
I don't think any GP9s came with 48" fans
That's not correct.
You can quickly check: http://utahrails.net/up/up-loco-features.php
There is a reference to when UP received 48" fan equipped GP9's.
I don't think any GP9s came with 48" fans. That was something that was started with the GP18/20s.
Nope. Many of the N&W GP9 units came with 48" cooling fans, especially the famous "Red Bird" passenger GP9 equipped with steam generators.
This Atlas GP7 model has 36" (3/4" dia.) cooling fans and a 48" (1" dia.) dynamic brake fan. You can compare the size. 48" Cooling fans would take most of the top hood, of either front or rear, of the dynamic brake blister.
?? Did one 48" cooling fan replace the (2) 36" fans ??, or was it (2) for (2)?
?? Did one 48" cooling fan replace the (2) 36" fans ??,
Yes, that's it exactly.
or was it (2) for (2)?
No, there was insufficient room for TWO 48" fans over each radiator section. Thus, all lets production GP9 units had the 48" cooling fans. For what it's worth, that 48" "fan" on the dynamic brake housing assembly was technically called a "DB Grid Blower", and NOT a "cooling fan", since it had a large DC electric motor driving the fan blades. The water cooling fans had a simple three phase AC variable speed motor.
?? Did one 48" cooling fan replace the (2) 36" fans ??,
Yes, that's it exactly.
or was it (2) for (2)?
No, there was insufficient room for TWO 48" fans over each radiator section. Thus, all lets production GP9 units had the 48" cooling fans. For what it's worth, that 48" "fan" on the dynamic brake housing assembly was technically called a "DB Grid Blower", and NOT a "cooling fan", since it had a large DC electric motor driving the fan blades. The water cooling fans had a simple three phase AC variable speed motor.
Thank you 
Mike CT
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