The plug I use for my 318 is the NGK GR4, part # NGK 2635, its a v-power resister plug easy to read, I like it best, just my preference..........good luck
NGK's seem to have the best Idle quality for any plug that I've run. Autolites seemed to be the worst.
I use NGK's GR5 in my 273 with the dual point distributor. I had tried an HEI conversion, but didnt seem to see the power difference other folks had seen, so went back to the dual point.
The GR4's were too hot for my compression ratio. GR4's seemed to do well on a lower compression 318 I was running for awhile. But went back to the GR5's after I got the 273 running again.