I've been meaning to ask the OP if he's gotten to run that 318 iron single plane intake and if so how well it worked out on the 273. I've got some old long time family friends who have recently joined the 273 club and are looking at intake upgrades.
I Freshened-Up My 273 Heads So I had to stay with the Original Intake for them. Your 318 Intake is sitting on a Shelf...
I was gonna buy the 302 Swirl Heads but 66FS talked me out of that.