as above really. what does it consist of to change the rear drums to discs set up? would you have to change the drive shafts etc

Usually you will need some discs , calipers and pads, some brackets and a different handbrake cable and hydraulic pipes/hoses.

probably would need you to tell us which axle you are using for more specific info.

it has a sierra diff (irs) and is running drums. i know il be needing discs pads and calipers. my main question is can i still use the drive shafts which are on it and just purchase the new uprights to take discs and new hubs, or have i got to get different drive shafts