An Easy Swap? 1970 C4 Into A 1967?

as long as you get the converter that goes with the trans, then you are good to go with the swap as it is a direct replacement. one thing to be careful of though is note the direction of the shift lever on the trans, it should match the one on your current trans to maintain the floor shift pattern. you could also swap to an after market shifter as well.

As far as the flexplate is concerned, as long as the '70 c4 is coming off a '70 302 it should have a 28oz imbalance just like your current one, so don't bother replacing it unless there is damage.