Another thing to pay attention to is the motor and trans mounts. I found in my 51 Chevy 2 dr sdn that drivetrain movement will contribute to missed and hard shifting. Just something else to look at. I have a 261 with a 235 head in it. Still using and loving the 3 on da tree. I actually broke a front motor mount. Replaced it and chained motor. I also drilled through both trans mounts and put a grade 8 bolt through em. Made all the difference in the world.Good luck. Dont overlook obvious issues. I usually find out the hard and more expensive way..