The smaller holes prevent overcooling. It was a problem on the early EAs so they changed the h/g to suit.
If the holes are enlarged, the head will not heat enough, will not expand, and will not seal properly resulting in poor gasket life.
Of course in a hi-performance engine that may no longer be true :) but for a stocker it's bad news. Been there done that
Proud TQE Operator and President of SEFAG - the Society for the Elimination of Ford Automatic Gearboxes
Pacemaker headers + 2.5" exhaust
EF Fairmont interior
Lowered King springs
5 speed manual
Newest mod: EF Ghia wiring loom and dash