looks okay
Did you change the years?
Try including it in the F-4C_loadout.ini on the correct pylon and load the game up.
comparing with another the only difference is your entry has SpecificStationCode= which you could take out - cant remember if that worked in SF1.
Make sure you are not flying in 1964 btw
[WeaponData030]
TypeName=SUU23
FullName=SUU-23/A Gun Pod
ModelName=suu-23
Mass=785.000000
Diameter=0.560000
Length=5.050000
AttachmentType=NATO,USAF,USN
NationName=USAF
StartYear=1965
EndYear=0
Availability=1
BaseQuantity=4
Exported=TRUE
ExportStartYear=1965
ExportEndYear=0
ExportAvailability=1
WeaponDataType=3
GunTypeName=20MM_M61A1
MaxRounds=1200
MuzzlePosition=0.000000,2.700000,0.060000
LightPosition=0.000000,2.800000,0.060000
AimDirection=0.000000,1.000000,0.000000
EjectShells=1
EjectPosition=0.000000,0.530000,-0.300000
EjectVelocity=0.000000,0.000000,-2.000000