As said above, Ford didn't use any gaskets at all between heads and iron headers on new 427s. But keep in mind that they were bolting two freshly-machined surfaces together.
When I put a freshly gone-through 390 into my '63 Effie ICB, the long headers were far from new and a bit worn. I chose to use the sort of gaskets that have a layer of gasket material on both sides of a sheet-metal perforated core. I also used stainless,, slightly-longer header bolts and stainless washers. The headers were bolted on completely before the engine/toploader was lowered into place. And I had someone on each side and another under the driver's-side floor to help everything go into place properly. Everything worked just fine, and I had a couple of wrenches made up that'd be of use to do a re-tightening job as the gaskets took a set over the first couple of weeks of driving.
I had no problem with leaks, and when I pulled the engine again after several years, everything was in good shape. If I had the same set of circumstances again, I'd do the same thing. Sometimes gaskets DO have a useful purpose.
KS