Make the saw holder out of something other than steel. Steel on your chain dulls it. This one was plastic I had laying around..complete with child handle to help my little one get on/off the machine.
Couldn't find a good place on the tractor so I made a mount for the box blade. The frame is metal, but has wood to protect the blade. Also made a wooden insert for the box blade to carry chains and other tools when cutting trees.
The search tool will often find useful information. Very valuable tool.
Here's a chainsaw mount I'm looking at. It was designed to be installed on a motorcycle, but they've adapted this one for a side by side. It appears to be an aluminum body with rubber/ plastic stop pads. As it comes, the scabbard will take a 16" bar, but additionally, you can order a 20" scabbard. This one comes with a right-angle mounting bar that could easily be adapted to a ROPS or crossbar installation.