LS4 and T-56?
I also own a 2006 Impala SS and like the motor!
The RWD bellhousing flange is also about 1/4" deeper into the block than the FWD pattern, so you will loose about 1/4" of effective bellhousing depth due to this. However, you also gain back about 10 mm due to the shorter LS4 crank... so you should end up with slightly more bellhousing depth/clutch room.
Mounting the starter would still be an issue, but is much easier with the 168 tooth RWD flywheel vs the LS4 142 tooth flex plate. If you had a flat plate between the engine/tranny you could run a face mounted starter.
Whether all this work would be worth it... depends entirely on the person and the projet goals.
If you wanted to switch to the 5 speed behind the 3800 camaros (4th gen), it would have the same bellhousing as the LS4 and would use a 142 tooth flywheel. The starter would almost have to go under the oil pan, but again it would be an option.
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