i moddified the files to get this to work several weeks ago but cant remember the files in question, i do know however that the game never CTD's but i've never seen 2 guys on deck even though i put 2 in the gun slots. i dont use this setup for game play i just like fiddling with files
i also believe you need to change one of the other files to make it work without the CTD i'll have a look see.
Below is what i've changed in my Balao file to get 40mm twins in the AA slots
personally its a bit mad so i prefer to use bow and stern 5.25's and twin 20's hehehehe.
here is a bit out of the balao upc file within upcunitsdata folder, think this is what your missing.
[UnitPart 2.UpgradePackSlot 1]
ID= UpgAAGun
NameDisplayable= Aft Anti-Aircraft Gun
Type=NULL
AcceptedTypes=USLightAA, USHeavyAA,
USDeckGun
UserCustomizable=Yes
IDLinkUpgradePackSlots= CTBackAA
IDLinkUpgradePackSlotsIntervalDefault1= NULL, NULL, NULL
[UnitPart 2.UpgradePackSlot 2]
ID= UpgBowAAGun
NameDisplayable= Fore Anti-Aircraft Gun
Type=NULL
AcceptedTypes=USLightAA, USHeavyAA,
USDeckGun
UserCustomizable=Yes
IDLinkUpgradePackSlots= CTForeAA
IDLinkUpgradePackSlotsIntervalDefault1= NULL, NULL, NULL
This is my other part from the upgradepacks.upc file
[UpgradePack 11]
ID= Upack40mmTwin
NameDisplayable= Twin 40mm AA Gun
FunctionalType= UpFTypeWeaponFlak
UpgradePackSlotType=
USDeckGun
Type=NULL
UnitUpgradePackIntervalOptionCurrent= NULL, NULL, 0
UnitUpgradePackIntervalOptions1= NULL, NULL, 100
IDLinkUpgradePackElements= 40mmTwinUS
Guys just noticed this extra bit... must have done this too... try this in addition to the other bits
; UpgradePackSlot (also in the unitparts3balao.upc file)
;
;************************************************* ***********
[UnitPart 1.UpgradePackSlot 1]
ID= UpgAAGun
NameDisplayable= Aft Anti-Aircraft Gun
Type=NULL
AcceptedTypes=USLightAA, USHeavyAA,
USDeckGun
UserCustomizable=Yes
IDLinkUpgradePackSlots= CTBackAA
IDLinkUpgradePackSlotsIntervalDefault1= NULL, NULL,
Upack40mmTwin
[UnitPart 1.UpgradePackSlot 2]
ID= UpgBowAAGun
NameDisplayable= Fore Anti-Aircraft Gun
Type=NULL
AcceptedTypes=USLightAA, USHeavyAA,
USDeckGun
UserCustomizable=Yes
IDLinkUpgradePackSlots= CTForeAA
IDLinkUpgradePackSlotsIntervalDefault1= NULL, NULL,
Upack40mmTwin