These very large scarab-like larvae were found under a rotting log in close association with Horned Passalus (Odontotaenius disjunctus) tunnels, and were originally misidentified by me as such. Horned Passalus grubs have a reduced third pair of legs. Thanks to whomever corrected my identification!

The large size of these larvae was notable, and suggests they were one of the few really large scarabaeiforms in this area. I think these are almost certainly stag beetles, Lucanidae, which has larvae very similar to scarabs--see UNL: "The larvae resemble those of Scarabaeidae, but in lucanids the anal opening is longitudinal or Y-shaped, whereas in scarabs it is usually transverse or occasionally Y-shaped."

I believe Lucanus is the only stag beetle large enough to have this large a grub in the area, so I am filing these under that genus. I've since found these same beetle larvae in my Durham yard, where I know Lucanus capreolus occurs. More photos of those specimens to be added.

Some links on Lucanidae larvae: stridulatory apparatus, habit of Lucanus cervus. Details of legs, etc. look very close.