I'm freshing my 355, it has low miles on it. On the top of the cylinder theres a ridge. I set a dial bore gauge down in the cyl and is at 4.031-4.0315 max. Do I need to have a reamer to take the ridge out or simple hone?

You should use a reamer. Actually, IIRC the tool is called a ridge cutter.
I think that a hone may not stay square, and could cause you problems.

On the other hand, it can be done.

Thanks, Thats what I was told on the hone as well.

Take something and see if the ridge is just carbon build up. If it is, you can just clean it off.

A ridge than small, you might be able to push the pistons past.