Depends on what year the 318 is. The "big cranks" started in 68 or 69, don't remember. You may need to find someone with a small lathe, they would be easy to make
All 318's I've ever seen have the large register for the torque converter. As far as I know, only the car '64-7 273's, and the '60-67 slant 6's were the only engines with a crank with the small register.
