As we now have the late Pfalz D.IIIa, with external guns, you can fix the old D.III with the correct burried guns by adding the following to the PfalzD3_DATA.ini replacing the old lines - It only remove the guns without changing anything.
[AircraftData]
EmptyMass=690.0
EmptyInertia=538.38,423.0,883.26
ReferenceArea=22.14
ReferenceSpan=8.40
ReferenceChord=1.53
CGPosition=0.00,0.00,0.00
OnGroundPitchAngle=11.5
UseMetricUnit=TRUE
DefaultArmorType=WOOD
DefaultArmorThickness=25
Component[001]=Fuselage
Component[002]=TopWingLeft
Component[003]=TopWingRight
Component[004]=TopWingMidLeft
Component[005]=TopWingMidRight
Component[006]=TopWingTipLeft
Component[007]=TopWingTipRight
Component[008]=BottomWingLeft
Component[009]=BottomWingRight
Component[010]=BottomWingMidLeft
Component[011]=BottomWingMidRight
Component[012]=BottomWingTipLeft
Component[013]=BottomWingTipRight
Component[014]=Tail
Component[015]=LeftStab
Component[016]=RightStab
Component[017]=VertTail
Component[018]=Nose
Component[019]=Remove1
Component[020]=Remove2
Component[021]=Remove3
Component[022]=Remove4
Component[023]=Remove5
Component[024]=Remove6
Component[025]=Remove7
Component[026]=Remove8
Component[027]=Remove9
Component[028]=Remove10
Component[029]=Remove11
Component[030]=Remove12
Component[031]=Remove13
Component[032]=Remove14
Component[033]=Remove15
Component[034]=Remove16
Component[035]=Remove17
Component[036]=Remove18
Component[037]=Remove19
Component[038]=Remove20
Component[039]=Remove21
Component[040]=Remove22
[Remove1]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Spandau
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove2]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Jacket
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove3]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Sight
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove4]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Muzzle
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove5]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Magazine
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove6]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Butt
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove7]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Butt_lever
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove8]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Drum
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove9]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Lever
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove10]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Lever_Handle
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove11]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Ammo_L
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove12]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Spandau01
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove13]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Jacket01
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove14]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Sight01
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove15]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Muzzle01
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove16]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Magazine01
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove17]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Butt01
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove18]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Butt_lever01
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove19]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Drum01
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove20]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Lever01
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove21]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Lever_Handle01
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
[Remove22]
//ParentComponentName=Fuselage
ModelNodename=Empty
DestroyedNodeName=Ammo_R
DetachWhenDestroyed=TRUE
HasAeroCoefficients=FALSE
Good luck!