removal of wheel cylinder nut.

[madaca]

Hey guys I am needing a little help. I am changing the drum brakes on my 65 chevy this weekend. I have never changed drums before. I took off one wheel today to see what I was in for and everything went well but I am having trouble taking off the wheel cylinder. I see there is a nut that is holding it on but I cant seem to get it off. Is there something I am not seeing or do I just need to use a little more muscle. I was afraid to put more muscle into it just in case there is something else holding it on that I am not aware of. Any help is appreciated. I will keep you all updated.