I also have a grandfather McJunkin from the upstate SC. I Know it's been awhile since your original post and don't know how much information you have found since then but... While looking for more information on Lucy Neville Mcjunkin I stumbled on to www.ourkinfolk
I still have little to nothing on Lucy but (if this site is accurate) it has the McJunkins going back to Ireland and Scottland. Samuel Sumter McJunkin (1813-1907) has a brother and a son named Henry. Hope this helps.