I don't know how much help this is but the engines are different in more than just displacement. I had a 2004 M800 (similar or same as your 620 for exhaust line-up) and it had an Arrow hi mount for a earlier 900 installed. Over the years I removed and reinstalled it a couple times and noticed that it was modified to fit. In my case it was just fudging with the mounting tabs. I suspect that you can make it fit.
As far as performance, I installed an Arrow titanium exhaust on my 620 Multi that can be used with either the 620 or 1000. Did not even have to remap. Sounds and runs perfectly.