2008 Challenger 6.1 swap input

Hey everyone I've finally decided to move forward with the HEMI swap and I've found a used 6.1 with 38k miles on it that I can pickup the entire setup for just under $5k locally. I've been reading a lot about these swap and doing the research, but ive also heard the charger/challenger transmission's require speed sensor inputs in order for the speedometer to function properly when the swap is done. Is this a well known fact or has there been any easy way to resolve the issue if it is a problem? Also any other red flags about the setup other then the standard hemi swap problems with shoving it into an "A" body? I made a thread because I'm looking at picking this setup up tomorrow. Thanks in advance guys.