It definetly needs to be correct if you don't want to have the trans clutches get worn out very fast. I also prefer to run reverse manual valve bodies in my muscle cars as I love to shift it when I want it to shift and I do race my car sometimes. I had a friend a few years back bring his 340 Challenger to me that he said would not shift right. And he was right as it had a Holley carb on it and linkage to the trans throttle pressure for who knows what. Once I got it set to shift ok the car was way off from full throttle as it was lucky to have 3/4 throttle. But the trans linkage was all messed up with a bunch of parts from different cars. I told him I need to get the right throttle pressure rods and linkage or get a good aftermarket setup to work right. He took it anyway that day as I set it to have good upshifts and shifted fine but no full throttle. Ron