I'm not super familiar with it. But from what I gather by looking at them in a number of cars it looks to use the hemi style cam, magneto etc. Being all billet it's really a custom design. Pretty sure the heads use the hemi bolt pattern but the heads are their own design that only share some characteristics of a BBC. The whole 481x came from Alan Johnson (Top Fuel genius). He took the top fuel hemi and used the BBC bore space to stay under a 5" bore and created a cylinder head that isn't a hemi head but is kinda sort of like a BBC big chief head. From my understanding in pro mod anything with a 5" bore spacing gets a lead weight trophy so this came about so guys could get the weight break of a smaller bore.
It is amazing what some of these guys can build from a big chunk of aluminum.
Having so many friends in the top fuel world I have met Allen a few times. We had a gathering of the minds on his Harley Billet heads. He is a freaking genius.