Dude if you want to seriously mod a C5, find a 2.7tt 6 speed. I am assuming you are going to try to pull your engine yourself in your parent's garage? Listen summer is coming up, you don't want to get over your head with the car apart not being able to drive it for months.

If you want to get more performance out of your 4.2, get the Giac engine and tip chip and Brembo brakes.

Back in Action, transmission fixed!

2000 A6 4.2 V8 (A6 Hulk)
Silver, Royal blue & Vanilla (rare)
5 spoke RS6 Rep 18's
Chrome side mirrors
Rear window spoiler
Modded Upper & Lower S6 Grill
Led tail lights, window tint 35%
Dual rear foglight mod
Led bulbs interior & exterior(so many!)
Resonator delete with chrome exhaust tips.
H Sport, front and rear
AIR horns with stock (fun)
JL Audio 1000/1 with 2 12" Fosgate P3 (too much too loud!)
Clear corner mod, (simple!)