A 63-66 slant will bolt right in. If you use a 67 slant, you will need to swap your 66 oil pan and pickup to the replacement motor. If the new motor is a 68-up, you will need to install the crank bushing to work with your 66 transmission's small snout torque converter in addition to swapping the oil pan/pickup. If your 66's carburetor is rod actuated, you will probably need to swap the carb as well or convert to the early A cable operated set-up. You might contact Charrlie_S who is in FL and deals in slants as well as sells the bushings I mentioned. Good luck on your search.
