I have swapped intake using both methods, drill the heads or drill the intake, drilling the intake is easier but turns out a lot uglier.

Also I don't remember if the V6 does this or not but the 360 TBI has the intake heated by coolant as well as exhaust. Either way I wouldn't worry about it as it would be fine even with no heat in the intake and it probably isn't driven in extreme cold either I'm guessing.