3.23 or 3.55 Behind a 318

Short stroke engines make their peak torque at a higher RPM. You need to keep that in mind when choosing a gear set. A 3.31" stroke (318 and 340) will want to spin some compared to a 3.58 (360) or a stroker. "I" would want my build to be just at the beginning of the torque peak at "whatever" cruise MPH I chose. If not, it's not going to be very efficient. Put a 3.23 or numerically lower gear set in a stock stroke 318 and it won't be very snappy at cruise speed. I would at least run a 3.55 or a 3.91 and preferably the 3.91 without an OD transmission. With the OD, then a 4.10, 4.30 or even a 4.56 will work well.