Swap details on what goes on to get a 4T80e to fit into a W-Body (GTP) 3800 combination. This is a 1998 Grand Prix 3800 supercharged car. It has the external range switch (neutral safety switch). With the large number of cheap cores one would think this swap would be more popular. If you are willing to put in the effort it works just fine and is cheap alternative to obsolete used GM Racing parts.

No cutting of the chassis harness was required. A jumper harness was made using some of the guidelines of LS4 King. This is not an LS4 car so I had to do a little verification to understand if this could work ahead of doing this swap.

Nobody produces the mounts for this swap. The swap is a bunch of fab work and welding. It is not that hard to do with a grinder and entry level welder. The transmission is a 2005, 3.11 gears, and without the internal manifold switch - this is easy to add if you want to add it in. Drill the valve body - it is spot faced but not drilled from the factory and mount your switch, pin in the wires. The transmission will not shift without using HP Tuners to adjust the ratio. edit- I did have success after looking into the tune again- the input tooth count was never changed.

Drive sprocket ratio - 1:1
Input pulses / rev - 39
Output pulses / mile - 23434 (for 3.11 diff)

Factory Cadillac axles fit the factory spindles on the W-Body. A boss on the engine bellhousing needs to be cut off the engine to make it made together. The driveline needs to be ~ 1 inch forward to make this fit on the subframe. I used a Bonneville (H-Body) front mount and a 4L80e energy suspension mount on the side.

   / @ls4king  

Willing to answer any questions and comments.