Previous poster is correct you simply connect the old wastegate feed to the new actuator. This isn't the ideal since it can 'theoretically' result in surging but I have never experienced this. I have a Turbo Technics VGT fitted to our Disco 2 but on it's own I doubt you would appreciate the cost / benefit ratio it simply wont add much bang for the buck on its own.
It does make the Disco a little more lively for sure but to get the most out of it you need to go much further - Intercooler, Fuel Mapping, remove the EGR and you may need to sort the air flow meter - the system can go into limp mode if the flow meter thinks too much air is being consumed. I simply added a 25mm bypass to supplement and limit flow through the meter since the flow meter is used only for EGR control it takes no part in the fuel equations - and I have no EGR.
The set up I run cost a shade over £2k. TT VGT Turbo, Allard Motorsport large intercooler, EGT removed replaced with silicon and stainless pipework, stainless downpipe (no cat), exhaust manifold trued up and refaced, decent quality manifold studs fitted, 5 Alive boost 'management' box, exhaust gas temperature monitoring and Auber instruments boost gauge, topped off with a remap from Dynachip, serviced the fuel system front to back and use Millers Ecomax cetane additive with all fills. I do have a straight through stainless centre pipe but can't be bothered fitting it.
The car (an 04 model 5 seat ES) currently believed to be around 200bhp and 340lbs/ft, I also get around 32mpg so that's better too.
It makes the Disco very 'driveable' but it still isn't so happy at and around 70mph - the TD5 just feels like it's under duress and the engine is still useless below 1000rpm (before it was useless below 1500rpm).
I did this primarily for towing but it still isn't enough to make me a TD5 fan. The power curve still forces me to use too many rpm and too much clutch to get the thing moving so I'm in the market for a Disco 3 TD6 or Range Rover at the moment.