Thank you for your response. The seller sent me a picture of the VIN plate, and the build sheet shows that it is a 2005 SRT6. The seller says that he is selling on consignment from a wealthy collector who is selling some cars from his collection. I have asked for more information, including which manual transmission was used, what fabrication was required, and how the ECU issues were addressed.

I was hopeful someone on this forum knew of this vehicle, which seems like a unicorn.

I have no problem with the NAG1 automatic transmission and in fact rather like it (I have a Dodge Nitro and a Chrysler 300 SRT8 that have it), but the idea of a manual SRT6 is intriguing.