Help choosing a v8 for my dart

And I almost forgot- you'll need a '66 column shift steering column (or convert to a floor shift) to replace the '65 cable shift column.
Edit: Now I see where you said your car is floor shift, but it still uses a shifter designed for the '65 cable shift transmission, you will need to find a shifter compatible with '66 and later transmissions- I believe the '66 is physically similar to yours, later factory shifters utilize a full-length console. Or go aftermarket. I believe there are threads on here about converting the Hurst ProMatic shifter to fit your early console.