I'm not the know it all Northstar guy around here, but from what I've seen most engine swaps do not end up well. It really all depends on what you want to get out of the car. However if it were me I would just keep the original motor and get the headgasket replaced.
My headgaskets went at 54k miles and they replace those, timeserted the motor, re-did all the seals, new motor mount, and quite a few other things. I've put another 16k on the motor and haven't experienced any trouble with the car since then.