IIRC, Glidden cut out the lifter galley and welded them back in and stood the lifter bores up to help with pushrod geometry. This was well before 48° blocks were available and is probably how they came about.
My brother has a 73 Mach 1 with a 351C 4V in it, I rebuilt it several years ago and was impressed with the size of the intake ports. A local bracket racer runs a 69 or 70 Mach 1 witha a 351C but he runs 2V heads, said he doesn't turn his engines enough rpm's to use the large ports, he also said his 2V heads pull better early in the run. He's won an a$$ load of money with that old car so I won't contest what he says.
