Rear Cam Case Bolt Removal

I am tearing down an O-320-E2A and am just about ready to split the case. I have what looks to be a camshaft with integral gear that is non removable.

What is the best way to remove the castle nut behind the gear? Is there a trick or special tool to reach it?

I use 2 short sockets on breaker bars. Cylinder wrench might get in there too.

I think a swivel socket would work well here.

Goosed up here

A Goose neck 12 point box-end, sometimes with a little bend in it. Getting it off is the easy part, putting it back on. Some times that takes an off-set deep box that has been worked on a little. It is old school but we used to call them shop made tools. I would use the Craftsman brand to modify the Snap-On ones cast to much. Yours. R.E.A. III #80888

Thanks for the suggestions guys. I was able to get it off with a goose neck 9/16" wrench.