Those are some pretty nice cattle. Really like the base width on a few of those heifer calves. I'd personally breed them to a Charolais bull to complete the cycle. Maybe even a black high stabilized % purebred Simmental would do the trick if you're looking for a black calf crop.
Breeding 3/4 bulls to half blood cows to arrive at the 5/8 3/8 is what both Brangus and Santa Gertrudis both did. Their success, though, should be attributed to the fact that they actually stabilized the cross at 5/8 3/8 before offering them as seed stock.