I dunno about the saab turbo, but we commonly get T25s and T25G's off of silvias all the time. That's a bolt up job. you will need to make a new downpipe to connect it to the exhaust though. and maybe need to clockt he turbo like you said. but the Stock T2 uses the standard T2 flanges.
Stock boost is around 7psi, but be sure to remove the pop-up valve if you're planning to run anything over 8psi. This valve vents to atmosphere if it goes over 8psi...it's a safety feature in case the wastegate fails.
I THINK the stock injectors are 270cc, but they can keep up. A few guys have been able to consistently run their motors with T25/Gs at over 12psi on the stock injectors and ecu. However, I'd think they were running near 100% duty cycle.
Running lots of boost on the ca18et is a bit hard because we suffer from having old engines. A common problem among the higher powered ca18et S12s is stretching the headbolts and blowing gaskets. Bartc_j has blown 3 headgaskets because of this problem. I believe ARP has stronger headbolts though.
Currently I'm running a standard ca18et @ 11psi and unintercooled. there has been no real adverse effects due to the increase in boost.
This is just basic info...there's tons more over at
http://www.club-s12.org/board and also the S12 section at SXOC
http://www.sxoc.com/vbb/forumdisplay.php?f=39 and probably aus12 as well
http://www.aus12.bb2.org/index.php