Hello
Download my IXB_Gunship_Vanilla_SH31.4_V2 it has two deck guns.
Use S3D editor for adding deck guns, look at my IXB gunship files for example.
Use right click for adding raw chunks = Gun nodes + look at cam and sim
files also. compare them for unmodded ones. Also look for treads how to use
S3D for SH3 and also for SH4 lot good info there. Good Luck