You need to use a 1/4" radius blue stone on the rotory machine you are going to use.
Like I said, sometimes you notch the block. The 427 blocks are notched for the intakes.
Stay back as far from the scribe line as you need to. Use a caliper to determine where the block edge is and mark that on the head.
The chamber casting is pretty thick there but absolutely any time you start grinding on iron heads you can get casting drop outs.
They are round pieces of buck shot like pellets in the castings and they will just drop out of the casting leaving a hole.
Lots of iron heads have been ruined by trying to enlarge the ports. There is some risk to it, yes.
The deck thickness of an unmilled Ford iron head SHOULD be about 5/8" thick. On occasion, they do have voids in the castings where you don't expect them to be or they shouldn't be.
You cannot look this stuff up in a reference book. Every head porter will have different experiences. You are already well past the norm and anything that you do now is proceeding at your own risk.
You might sail through 8 cylinders and just as you go to the last one, an unexpected occurrence will happen that will set you back.
When you get through these modifications with no issues, I am of the opinion that you have no way of knowing whether or not you were just lucky or good?
This is why I say if you DO NOT NEED this work, DON'T DO IT.
in addition, you might not have ANY problems now until you run the engine, then you could crack through a thin part of the casting.
Lots of ported heads will develope cracks around the valves or even just a porosity. Then you have to take the head off, weld it with stainless rods, then polish the weld off, then run it again...then it might crack again.
Like "Dirty Harry" said, "do you feel lucky today?"
