Ken,
I believe my own Kentucky relatives spelled it Holcomb and Holcombe before the war. You bring up an interesting point about spelling. The rate of literacy amongst Southerners was lower than anywhere else in the country around 1860.. I think only about 80% of whites were supposedly literate compare to 95% in the Mid-West and 99% in New England...every white New England adult unless mentally impaired was literate. Though this is the modern age, I quite frankly doubt that this will be matched again...public education being what it was. However I think that reading skills might (I say might) have been a little higher in the South than most think. Folks even in the backwoods could read the Bible. It is possible to read very well but have a miserable hand at writing and even spelling. I'm not bragging but I've been a very studious student of Shakespeare in my time and devoured books like a fat man eating chicken. That said, my spelling is not the best and my handwriting is frankly deplorable. Looking at it, you would think a Fourth Grader was writing. So I believe (heck I know) that it's possible to read very well but when it comes to writing it would look like something a chicken would scratch in the dirt.
James.