I can't recall any evidence of Liberty ships with a 5 in gun forward. The Trumpeter kit has a smaller, 3 or 4 inch gun forward, 5 inch aft. Many of the pics show a 3 or 4 inch gun aft with only another 20 mm Oerlikon in the forward tub, which corresponds to the info on U-Boat.net.
There could well have been .30 cal machine guns too.
Just guessing, but it would seem to be unlikely that a Liberty would get new guns fitted after launching, especially as late in the war as 1945.
Fred
PS I have a similar project in mind. My father served on the Liberty Frank O. Peterson in 1945, taking P-38s to Biak in the SW Pacific. I want to do a diorama of the ship unloading. When I ask him about details of the dock area, he looks at me like I'm nuts. "It was a dock! What else am I supposed to remember from 64 years ago?"