It's not the same corn.
All you need to know: corn = Archer-Daniels-Midland = Iowa primary = ethanol subsidy.

W/r/t "Seems like the squish in a Hemi is in the piston dome on either side of the valve notches. How close can you make them fit the chambers? .040"-.060" clearance, smaller radius than the chamber"
In some British bikes it is, but the dome shape has to be really accurate. Making it out of an existing piston would need more positive deck or a head mill (!!), and removing some of the dome volume at 12 o'clock to keep the CR.
Even if you don't get actual quench (something no wider than about .060"), you can get squish (higher turbulence) by simply making the piston dome radius curve away from the chamber wall as it approaches the plug - the charge will flow to the larger volume.
You might be able to build some swirl into that as well, but:
1. would you want to?
2. which direction?

Gold Star, Manx, G80 500 singles are much easier to work on!