The problem with mixing and matching transmissions, manual for auto and vice versa, is that the PCM still looks for inputs from the transmission. You'd have to find a way to fake the computer into believing the same type of transmission is there. It's wired into the stability programming, security system, as well as the powertrain module. This was one of the big reasons HDDP went with the Bosch controller, you don't have to worry about that stuff anymore.

The flex-plate has a different bolt pattern than the flywheel where it mates up to the crankshaft.

A SRT swap is no problem if you take every last piece of the mechanical parts as well as every bit of electronics. After all, the body dimensions are the same SRT to non-SRT, but every single thing under the hood and how it operates is different.

As far as knowing if the manual trans is up to the power of the SRT engine....I have no idea. HDDP did it after a LOT of effort and money, but his is a track car, he expects things to break.