Amend the entire planting bed with substantial amounts of organic (as in once alive) material. Compost, shredded leaves, soil conditioner (which is mostly composted bark), bark fines, etc. Then select a good organic mulch to apply over the soil when the planting is done.

I'd avoid plain peat moss as an amendment. With the exception of the shredded leaves, you can purchase all of the above (and more) from garden centers or home improvement stores. I really like the 'Soil Conditioner' stuff (either at Lowe's or Home Depot).

Clay, especially red clay, has two attributes that Dryopteris cycadina(atrata) doesn't tolerate. High acidity and poor drainage. They will also need some shade, either full shade or partial. rhizo_1 has good advice, for planting almost everything in clay, that requires good drainage and neutral to slightly acidic soil.
After planting, keep them moist, not soggy, until they become established. They are a rather fast growing species and will rapidly develop into a large specimen.
Enjoy!
Rb

I am thinking that we will dig out the whole area about a foot or two down and replace the clay with lots of organic material. should we put down a layer of rock just to add a little more for drainage?

I wouldn't replace the soil. Just incorporate a great deal of organic material IN to your clay. You'll simply create a bathtub filled with muck if you try to replace it. Water will be 'very' slow to leave the basin of organic matter. Clay is not necessarily bad. It simply needs to be amended. No, to the rock, too. A layer of rock will do the exact opposit of what you want. ;-)

The fine particles will clog up the rock and soon form a barrier that water will find more difficult to move through than plain clay.

Do you know the native pH of your soil? If not, take some samples now, before amending with some good organic matter. Extension office are probably busy at this time of year, but you should have some results in a couple of weeks.