A modern '09 & up Hemi with a 904? Are you going to keep the soft suspension, flexible chassis and 9" drum brakes to match that 904? Forgive for the sarcasm, but why no overdrive?
You are more than welcome to cut my floor up and patch it back up if you would like to do the work.
I don't need the extra pain in my life, I main decide to go a different route later, but at the moment I have a 1500 dollar transmission and converter....That I will be using.
Below are my options for Auto:
Automatics:
904 or 727 both can easily built to handle the torque and HP of a Hemi. No modifications to floor pan. Though you do need to shim the trans .060 as the modern Hemi has a different off-set. Bouchillon Performance and many others sell the spacer. Otherwise it is a direct bolt up.
A518 has an overdrive and as others have pointed out requires floor surgery, though not nearly as much as a RFE545. Does NOT require a computer. Can easily be built to handle the torque/HP of a modern Hemi. Like the 727/904 you should shim trans.
RFE 545 Stock Hemi trans. The truck/SUV trans has the speed sensors built into the trans so it is the easiest to retrofit into a muscle car. Hot-Wire can build you a wiring harness to use the truck transmission behind your hemi. Benefits a five speed with two overdrives. Requires SIGNIFICANT tunnel surgery, along with a custom cross member.
The RFE 545 is a weak link and requires a lot of work. I would do the work...but is a weak link for my power. The 518 would be the only other choice from a 904. So if you read the original post, and saw my possible decisions for power making, you would know why I am doing 904.
There is always gear vendors too.