Thanks to all for their suggestions.
The Myrlte Beach highlight was Bistro 217 in Pawley's Island - terrific food, reasonable price. We also enjoyed Capt. Dave's in Murrell's Inlet, although we had probably lingered too long by the blazing fire in Bubba's Love Shack next door (good pimento cheese, good hush puppies, ill-conceived pickled shrimp.) A surprise hit was Goodfella's in NMB -- the 55 cent oysters were great as was the "Chumbo" - a combination of chowder and gumbo that was much better than it sounds. And we had a good breakfast at Dino's, also n NMB.
In Hilton Head we had a wonderful dinner at the Old Fort Pub, which had a 3 courses/$33 special. Excellent charcuterie plate and best-ever shrimp and grits with top-quality tasso were highlights. We also had excellent meals at Hudson's (but their hushpuppies are pretty bad), Skull Creek Boatyard (try the fish taco appetizer, or get it twice at the bar ($2 off) for a full meal, and Michael Anthony's (chicken marsala was very well prepared; saltimbocca was good also), and at the black marlin. - and a pretty good breakfast at the Hilton Head Diner (home fries had far too few, if any onions). The big disappointment was Roastfish and Cornbread which, unbeknownst to me, had lost its liquor license, and they had taken their very good gumbo off the menu. You can BYOB (so now you know) but that's a limiting issue when everyone prefers to drink something different.)
We had day trips to Savannah, where Wylie's has excellent barbecue, fried okra and macaroni and cheese (avoid the green beans and the cole slaw), and to Beaufort, where Plum's was a disappointment. The gumbo had a distinctive cumin taste and the shrimp po boy had good shrimp and good bread, but only about 5 of them, so it was a lettuce and winter tomato-dominated sandwich.