I am getting ready to start a 2004 5.7 with a 545rfe into a 71 challenger project. I've researched it a lot, I've heard the trany tunnel needs to be expanded, but can be massaged with a hammer where needed. I plan on cutting the tunnel out, then cutting it down the middle and adding what I need there. Also raise it up some as needed. The trany does NOT have a speed sensor in it, and I am still undecided as to what I am going to do for a speedo. Untill I figure it out, I am just going to use my GPS. From everything that I've heard, the 545 is a 3 speed auto with an electronic double overdrive. If I have it right, my 3 speed slap stick will work with a cable insted of linkage, but I will have to add an electric button to enable or disable the overdrive. I still have a lot to figure out, but I also already have a lot figured out. Please correct me if I am wrong on the shifter or anything else that I mentioned. PM me if you have any specific questions that you are not getting answers for here.