Dolmar 143 with 123 muffler

[Massey]

Hi there , recently I finished my 143 but it came with a muffler from a 123 maybe (doesn't have trace of the little piece where the bolt hold it on chassis left side ) so would it need to opened up a bit ? I don't want to make it too hot on this new top end but I made some cuts with and it didn't seem to with 20 inch bar.
Thank you by advance

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