to change the column used to pass the name, edit this line on the checkout page:
$WA_PP_ECO_Do_itemized[0][$nextIndex] = "Name" . strval($cartIndex+1) . "";
$WA_PP_ECO_Do_itemized[1][$nextIndex] = "".$siteCart->DisplayInfo("Name") ."";
if you named the calculation "productName", change that code to:
$WA_PP_ECO_Do_itemized[0][$nextIndex] = "Name" . strval($cartIndex+1) . "";
$WA_PP_ECO_Do_itemized[1][$nextIndex] = "".$siteCart->DisplayInfo("productName") ."";