It can be a serious pain to get a feed neck off...
You'll probably need a strap wrench, unless you're willing to crap up the stock feed neck.
I had a strap wrench and still couldn't get the feed neck off my IR3. I ended up drilling a hole through both sides of the feed, and torquing it off with an allen wrench.
And then it turned out the feed neck I had was too low to allow the breech to swing open. What a treat.
I eventually got one that worked, but let it be a warning, take it slow, look over each step, make sure it all will make sense before you do anything permanent.