ikar01
For some time I gave up on PT Boats because it seems the only one they ever put out is the 109. Didn't they put a 20mm up front on their last trip?
There have been short-run "cottage industry" kits out there. And the "running" boat companies like Dumas have issued kits of different boats.
There's a bit of a complication, too, in that there are three different vessels in the "PT Boat" genere, and two major builders. So, there's Elco, and there's Higgins as builders. Then, you (very, very broadly) 770, 77, and 80 foot long boats. Pretty much all of those used a trio of V-12 engines each driving its own prop, and either dual or triple rudders.
The deckhouses and gun tubs all varied at least some between them all.
In theater, some of the "Peter Tare" crews would "acquire" weapons that better reflected their need to engage barge and coaster traffic--targets not appropriate for expensive torpedoes (recall, too, the torpedoes wer still hand made, one at a time at the Torpedo Factory, and were not a "sure thing.") So, a number of Army/War Department field guns would be "unofficially" added to the boats.
The current wisdom, taken from contemporary written accounts, is that 109 had an M-3 37mm anti tank gun, wheels removed, and strapped to large lumber planks (circa 2x8 or 2x10). This is what the RoG kit depicts, including the sheet metal gunshield (which was not very common in the various boat Squadrons, per photos and written accounts). This was a 57 caliber barre using the 37x223 Rimmed AT round.
There is some speculation that 109 might have had the M-1 37mm anti-aircraft gun--a 54 caliber barrel firing the 37x223SR round (these were not interchangable).
The 37mm AA gun was not very effective in the AA role, so they would be more "surplus" to needs than the AT gun, which was very effective aginst Japanese armor, trucks, bunkers and the like.
Later PTs would get a mount using the M-4 Autocannon an aircraft mounting (famously in the P-39) using the 37x145R round and a "horseshoe" magazine.
To further complicate things, most of the PTs did not much outlast the war. So, for the TV shows, 60 & 70 foot "Crash Rescue Boats" (all built to AAF cointracts rather than Navy Department ones) were used as "stand ins" often with extensive remodeling.
The AAF boats were retained past 1948 and the creation of the USAF, so were available to use in movies and tv. The hul forms wer simpler, but they were typically twin V-12 powered.
There's far more historical detail than that, too.