Engine swap for 100Q

Hi to all, am new to this and have many questions.  I drive a 92 100 quattro with a 5spd.  Great car but wish to get little more HP.  Car has 200k plus miles and the engine is a little tired.   I am considering an engine swap.  I know the results will not be huge but I thought this might be a fun project, providing this is doable.

 I would like to go from 2.8L 12 valve to 2.8L 30 valve (non-turbo).  I have access to 98 VW Passat engine with control module and harness.    

My questions are: Are the V6 blocks the same from 1992 through 2000?  Is there any major difference from VW to Audi? Any info or references are appreciated, thanks

not much difference from vw to audi, but there is a huge difference between the 12v and the 30v engine.  It's not worth the cost.  You will end up sinking thousands and thousands.  Totally different electronics harnesses, ecu.  Basically its been thrown around many times, and it was never an economically sound project. 

Would like to hear more of the difficulties of this conversion.  I assume engines can come complete with controle mudule and harness,  It is my understanding that I would have to find a home for the new module.  I also assume some wires will have to be traced and "patched" in.

Keep in mind that I would only consider an engine from1998-2000, as later models have wiring harnesses that tie to the instrument cluster, some sort of anti-theft device?.

I have been recieving my info from a fairly seasoned Audi mechanic but he does not have me entirley convinced of the project.  That is what has brought me here to this sounding board.

So please, continue to show me where the problems will be, 

Thanks to all who reply

I'm not a mechanic so I can't give you the specifics of why it really hasn't been done.  So you have a car with 200k miles on it that is only worth a few thousand right? You want to drop in a say $4000 dollar engine into it?  And then on top of that you will need to spend several thousand more getting all the pieces parts that the car will need.  Keep in mind Everything in your car is not ODBII complient, the 30v and all its parts are.  If its purely a project car and you just want to have some fun (money not being an object), go for it!  It would be interesting to do.  These are purely my opinions though, don't believe everything I say!