The catalog description seems ambiguous to me.
One person on my old thread suggested that they were recreating the old Indian River broiler cross -- though why they wouldn't just use that name I have no idea (maybe it's patented?).
Let me find that old thread .....
https://www.backyardchickens.com/threads/has-anyone-raised-murray-mcmurrays-delaware-broilers.1409619/
Here's the first post from a person interacting with Murray McMurray's customer service...
Just a note. I looked into these and found that they are NOT broiler-strain, heritage-type Delawares. They are a crossbreed that don't breed true.
@Tre3hugger, where did you get your broiler-strain Delawares?
You *could* replicate it if you bred millions of birds over 50-some years with...