Hi Ricky
I know itis not a disco but I have almost finished a 4 inch in a defender very similar to a disco when it comes to suspension. You will need the drive shaft you will need to correct the castor angle, with castor bushes or radius arms, brakelines will also need to be change and the panhard rod for an ajustable one as the wheels do not sit center under the car. If you are still running with a sway bar then this can be dropped off but body roll is quite sever to compensate this I am useing large big bore ajustable
Shocks , the large size helps to stop the body roll with out fade(thats the idea). The rear of the truck is getting the same treatment just waiting on the parts. Inside the springs at the rear are polyair bags to combat the body roll factor. The reason for everything being ajustable is that on road you can stiffen up the car then off road let the air out of the bags change the dampening on the shocks and all of a sudden it is loose and flexible. This is in a defender but I have had similar lifts in a hilux and also a rocky and the same type of body roll was experienced and the same parts on all three cars having to be replaced. But by choosing the right parts and not skimping on the dollars ie buying some thing cause it might do the job always go for the things that will do the job saves you money in the long run and the car will remain driveable, safe and also in OZ help getting an enginear's certificate. (needed for this kind of modification in OZ)
Try this link for spacer install. was easy as piss.
Link
With all things how big is the check book as 4 inches is costing a bit. This is in aus
Shocks $1000
Castor Bushes $180
Spacers $100
Polyair (Ebay) $60
Bolts bits and pieces $50
Panhard rod ( around )$180
Drive shaft waiting on price
brake lines waiting on price
and enginers cert between $500 and $800
I know you were not after prices but this is just a guide for anyone else thinking of doing it.
Here is some serious lift buy those crazy arctic
guys
I know it is more info than you asked for but hay what can I say.
Adam