Correct me if I am wrong but as far as I knew a 318-3 was a heavy duty truck motor and had a steel crank in it and fully floating rods as well as other strength parts.
The motor in my son's car in the Avatar, has a stage 3 truck crank in a 340, - should be balanced, but isn't, we threw it together with Frankenstein parts to run one weekend. Still in there several years and races later. 13.19 iirc, it ran so well we left it alone. No drama.
We're building a stroker for it .
No noticeable shake or vibration, flame on .
Pic #26 shows the difference between the standard and 340 cranks, with the hole thru the front and back throw
I am in no way suggesting not balancing is acceptable.
I often experiment with my own chit !