'92 SSEi 148,000 (km)

Last Fall, (around 5 months after purchase mind you) I ran into horrible problems with my Bonneville. A mechanic friend told me it was the crankshaft (thats as specific as he got) and it had to be repaired immediatly. Technicly the car still ran at the time, but it would shudder hard while idleing, made a noticeable knocking sound like metal on metal and was obviously 'screwed'. Since, the car has sat in my yard and now I'm finally able to put some money into it and try and get it back on the road.
I have a few questions reguarding this. First off, is it even worth replacing this part ? or should I look into getting a new engine. And if so would I have to get the same engine ?(same year, etc..)
And one last thing. If I was able to get my hands on a used 3800 series II engine out of a newer Bonneville, LeSaber .... whatever, would I be able to put that engine in my car and put the supercharger on that one(or jsut leave it off). And if it is possible, would I run into any major hang ups in the process ?
I have several friends who are willing to do the work for basically a few cases of beer and a bit of cash and i trust their work, but I would like to know what my options are before I start throwin around cash.
Obviously I know little about the inner workings of cars, so please don't laugh.... I'm jsut trying to find out where I stand on this.
If any advice could be offered it would be much appriciated.
Thanks.

First off, get another mechanic. If he won't give you more info than "it'* the crankshaft," I wouldn't want to deal with him. He probably meant that a rod bearing is knocking, which is bad.
Find a better mechanic who will give you more info.
Others here will know more than me, but a Series I to a Series II swap is more complicated than just dropping the engine in. The computers are different, the way they control the engine and tranny is different, and some trannies are different.

That supercharger is an M62 and will only fit on a Series 1 engine designed to handle the supercharger. It will not work on the standard Series 1 engine, nor any of the Series II engines (uses an M90). I would get a second opinion from a good mechanic.

I would say that the easiest engines to swap in there would be a supercharged Series 1 from a 92 or 93, but all of them could fit in there with additional effort. Whatever you do, bring the original computer with the engine.