Take a look at my site for the Drennan/en/on Resources that I have loaded there. I cant guarantee that there's anything to help you but there's always a chance. I also have links to other Drennen/an/on websites that are on the net that may help you in your search for your Drennen/an/on ancestors. By the way they also spelled their names Drenning/Drinnen/on/an.
Happy hunting and if by chance there is a line that matches yours would love to include your line.