Any special advice on this topic? I figured I'll break the weapon down and work on just the lower, removing the buffer and buffer spring first. I ordered the spanner wrench the other day it does not look like a complicated thing to do. I thought I'd make a small registration mark on the nut & the lower before I start so I can know where to tighten it back to. If anybody experienced on this has any tips or advice I would welcome it. Thanks.

I would suggest first figuring out if the castle nut / end plate combination have been staked.   If so.... have fun.   Otherwise, it is cake.

Read this thread about how great is to make sure your castle nut is staked.

Thanks. It was a simple job.