"18 degree heads? Can you enlighten us as to what those are?"
18 degree heads are....er....well....they are....er.....you know....well...
let's just say they are not "Ford" related and let it go at that.
P.S. "18 degree" refers to the angle of the intake valve (stem centerline) to the centerline of piston travel.
Original heads had a 23 degree angle on this (cough, cough) manufacturer's small block engine.
.........O.K. I'm coming out of the closet here.....I LIKE small block Chevy engines! There, I said it!