Here's an important item that you will need also. An engine! We are sourcing ours from a less fortunate Audi S6. I believe that it is a 1996 vintage, but the year that you pick really depends on your personal preference. I hear that any of the I5 motors would work in this swap, it is just a matter of how you want the motor to be equipped. I personally was looking for an S4 or S6 built between 1992-1997. You'll find that S4's were built until about 1994 and then renamed S6. In the 1997-1998 time frame a different engine started being used. Before the S4/S6 series there was a Audi 200 20vt that was made in 1990 and 1991, I think. So if my dates are wrong shoot me a message and I will correct them. In this configuration there seems to be a distributor and a different intake manifold. Older than these are Audi 10vt cars which are also usable.
The reason that I chose the model I did was because it has no distributor and the intake manifold begins on the driver's side of the engine. The Audi 200 20vt has a distributor and the intake manifold begins on the passenger side of the engine. Obviously the S4/S6 power plant is a closer match to how your 944 is configured right now. I'm making the assumption that this will make all of the intercooler plumbing easier to install.