Which 318 should I build ?

Both are very similar. The IH block casting should be a good one. (cast in a International Harvester foundry)
I totally missed that! Good call. Knew they were out there but the first time I seen it in the wild. My vote is now for the IH block with the 78 heads. I figure the IH plant was probably not as balls to the walls for production figures so they may have been a little sharper in the tooling and a little slower on the line?