DSC-off wrote:

I can't help with the original question sorry.

There are advantages and disadvantages to both types of castor correction.
Both methods rotate the king pin and swivel bearings, supposedly back to factory specification or near to it, to restore the original steering geometry and handling of a vehicle with lifted suspension. The angles and loads going into the king pins and bearings SHOULD be the same with both methods.

Using castor corrected suspension arms will rotate the whole axle backwards, changing the angle of the differential in relation to the propshaft. The universal joints in the prop will be working at a greater angle all of the time and will wear out quicker. Driveline vibration is another possible effect, worse than only lifting the vehicle.
It will however improve the alignment of the chassis bushes and panhard rod bushes, as they are normally twisted and preloaded on a lifted vehicle.

Castor corrected swivels leave the Driveline angles as standard, the relationship between the differential and the propshaft. (Except it is lifted, and therefore a little worse at the transferbox end) The rotation of the swivels, due the bolt hole position, changes only the king pin angle and leaves all the suspension mounts on the axle unchanged. Panhard rod bushes will wear more quickly.

Both methods are not adjustable if it doesn't work. Both methods involve fitting non standard parts to the vehicle and will require removal if the suspension height is later changed back to standard.

RobM wrote:

... The plan was to buy 2x of the FTC5366 and have them slotted to correct my castor issues...

RobM wrote:

Hey guys...
I'm also going to replace the front prop-shaft with a Gwyn Lewis DC prop-shaft as the vehicle is lifted but too extreme (50mm > 75mm maybe, hard to say not knowing what factory height is)

Since I'm having to replace the Swivel housing balls and basically having little to no castor & speaking to other LR mechanics/suppliers, I thought this option would be the best solution as I use my Defender mainly for Remote Touring, etc

As mentioned - replacing the radius arms will make the prop-shaft angles worse

If it was my vehicle that had a 3" lift the additional mods would be,
Caster corrected swivels. (not slotted)
Double cardan front prop.
Adjustable panhard rod.
Plus, if you can find or make them, radius arms to correct the suspension bush angle at the chassis end. WITHOUT any caster correction. I've never seen any of these for sale or know of any company that makes them.