Sometimes we saw 大二爺伯 of the 5th court at CCK cemetery.
I always think that they are 谢必安 (General Chia) and 范无救 (General Fan). Perhaps each court has their own 大二爺伯 like what you say.
I used to read travels in Hell by Gigong when I was a young apprentice at a temple
Chapter 49 :
Hell messengers are of two type : Black and White, sometimes called 7th Master and 8th Master, Sometimes called "No help Fan", "Sure Die Chia". For those sinners, these messengers of hell will appear hideous. For those pure in heart, they will see without fear, hence the saying, if you don't do wrong, even if someone knock at midnight, one will not be afraid.
Those interested to read the full book of Travels in Hell (in Chinese), please refer here :http://www.webhope.info/lcbook/Dy/Dy.html
For English : http://www.webhope.info/lcbook/English1/E-Dy/e52a.html