M6 to an TH350
M6 to an TH350 
The person im getting the trans from is trading me even and doing the work for free he is giving me a trans temp guage, pedels ect... it has a 3600 stall should that be good for what i have thanks.
Here is what I learned from converting my A4 1998 Z28 to a TH400:
- You can use your stock flywheel, provided it has the dual pattern. I don't recall it on my 2001, but the 1998 had the SBC converter bolt pattern. Just requires 1/8" spacers.
- The TH350/400 will bolt up using the side bolts along the alignment pins, the bottom three and center top one are not used.
- You'll need a shifter for a TH350/400.
- You'll need the VSS from a 3sp 4L80 (the non-electronic trans in the late model trucks). This is available from GM.
- Since yours is an M6, you'll need to correct the speedo by multipling it 2.5 times. A4 going to A3 need only a connector to plug into the 3sp VSS I mentioned above.
- You need a spacer for the OEM trans mount to work. I just bought a BMR K-member and solid mount for the trans.
- You will need to lengthen your driveshaft to work. Be sure you do not need the large TH400 slip yoke, the 4L60E one will not work. It will work on a TH350 though. Not an issue with M6 conversions.
- You will need a dipstick tube, I chose the Lokar flexible, firewall mounted one from SummitRacing.
- Finally, you'll need to get a torque arm that uses an aftermarket TQ arm mount, or one that incoporates the trans x-member as well.