So you can't really see whether it causes a restriction or not. Wonder why the PD150 needs two silencers
From what I saw when I did mine, I'd cut yours like in the attachment. If it's anything like the 210/225 one the smaller diameter tube fits inside the larger diameter tube/cannister, then they're welded together. So if you grind through the cannister only and not the inner tube it should come apart. I was thinking this, 'cos if it all goes horribly wrong then you could easily weld it back up.
Measure the distance between the inlet and outlet first though...