Ok, below are the config files for those two parts, and I'm linking more screenshots of those two parts individually. Apparently, I can mount the tank on the side, or superimpose it over the adapter, but can't put it underneath... Strange.
http://imgur.com/a/VnRG6
Adapter
PART
{
name = Size3to2Adapter
module = Part
author = Squad
mesh = Size3Adapter.mu
rescaleFactor = 1
node_stack_top = 0.0, 1.1, 0.0, 0.0, 1.0, 0.0, 2
node_stack_bottom = 0.0, -1.1, 0.0, 0.0, -1.0, 0.0, 3
buoyancy = 0.375
TechRequired = largeVolumeContainment
entryCost = 8800
cost = 2600
category = Structural
subcategory = 0
title = Kerbodyne ADTP-2-3
manufacturer = Kerbodyne
description = This adapter is used to bridge between Kerbodyne and Rockomax rocket bodies.
attachRules = 1,0,1,1,0
mass = 0.2
dragModelType = default
maximum_drag = 0.2
minimum_drag = 0.3
angularDrag = 2
crashTolerance = 6
breakingForce = 200
breakingTorque = 200
maxTemp = 2000 // = 2900
bulkheadProfiles = size2, size3
tags = cone rockomax
DRAG_CUBE
{
cube = Default, 7.344658,0.7515181,1.980434, 7.344658,0.7516301,1.980434, 11.00077,0.4258759,2.35452, 11.00077,0.7470945,0.1906485, 7.3984,0.7432775,1.971122, 7.3984,0.7581861,1.971122, -1.907349E-06,0,0, 3.776463,2.301678,3.757764
}
}
Kerbodyne Tank
PART
{
name = Size3LargeTank
module = Part
author = Squad
rescaleFactor = 1
node_stack_top = 0.0, 3.74, 0.0, 0.0, 1.0, 0.0, 3
node_stack_bottom = 0.0, -3.74, 0.0, 0.0, -1.0, 0.0, 3
node_attach = 0.0, 0.0, -1.89, 0.0, 0.0, 1.0
TechRequired = highPerformanceFuelSystems
entryCost = 46600
cost = 13000
category = Propulsion
subcategory = 0
title = Kerbodyne S3-14400 Tank
manufacturer = Kerbodyne
description = When nobody believed in (or even asked for) an even larger fuel tank than the already enormous S3-7200, Kerbodyne stepped up with the sanity-defying S3-14400 model. Carrying fully twice as much fuel as before, this fuel tank may just pack enough propellant to justify its proportionately enormous cost.
attachRules = 1,1,1,1,0
mass = 9
dragModelType = default
maximum_drag = 0.2
minimum_drag = 0.3
angularDrag = 2
crashTolerance = 6
breakingForce = 400
breakingTorque = 400
maxTemp = 2000 // = 2900
bulkheadProfiles = size3, srf
tags = fuel fueltank ?lfo propellant rocket
MODEL
{
model = Squad/Parts/FuelTank/Size3Tanks/Size3LargeTank
}
RESOURCE
{
name = LiquidFuel
amount = 6480
maxAmount = 6480
}
RESOURCE
{
name = Oxidizer
amount = 7920
maxAmount = 7920
}
}
Interesting enough, there's also a folder in FuelTank called Size3LargeTank with a part.cfg, maybe from an older distribution? In case you're curious, here it is:
PART
{
name = Size3LargeTank
module = Part
author = Squad
mesh = Size3LargeTank.mu
rescaleFactor = 1
node_stack_top = 0.0, 3.74, 0.0, 0.0, 1.0, 0.0, 3
node_stack_bottom = 0.0, -3.74, 0.0, 0.0, -1.0, 0.0, 3
node_attach = 0.0, 0.0, -1.89, 0.0, 0.0, 1.0
TechRequired = highPerformanceFuelSystems
entryCost = 46600
cost = 13000
category = Propulsion
subcategory = 0
title = Kerbodyne S3-14400 Tank
manufacturer = Kerbodyne
description = When nobody believed in (or even asked for) an even larger fuel tank than the already enormous S3-7200, Kerbodyne stepped up with the sanity-defying S3-14400 model. Carrying fully twice as much fuel as before, this fuel tank may just pack enough propellant to justify its proportionately enormous cost.
attachRules = 1,1,1,1,0
mass = 9
dragModelType = default
maximum_drag = 0.2
minimum_drag = 0.3
angularDrag = 2
crashTolerance = 6
breakingForce = 400
breakingTorque = 400
maxTemp = 2000 // = 2900
bulkheadProfiles = size3, srf
RESOURCE
{
name = LiquidFuel
amount = 6480
maxAmount = 6480
}
RESOURCE
{
name = Oxidizer
amount = 7920
maxAmount = 7920
}
}