If you can get hold of the larger 308mm caliper hangers as found on the gsi or coupe turbo then you can use the standard calipers fitted to the 2.2 and just chuck on the 308mm discs. You wouldnt even have to touch a hydrolic pipe. once youve got the bits it should only take you a couple of hours to do max. I'm sure a lad on Astra sport who worked for vauxhall was offering the hangers cheap.
As for 308mm discs, the groved ones regal sell are a standard Saab part. I'm not sure which model or part number they were, but you could get them from the likes of europarts a lot cheaper then from anywhere else.
found a link for you!
http://www.m1gst.com/vb/showthread.php?t=55928