When converting a single engine to a multi and using similar total displacement as a multi to the single engine version there will be a performance gain realized. This is because when divideing the same relative power into, in your case three propellers has the effect of reducing the propeller disc loading which is similar to the effect of using a larger diameter lower pitch prop on a single. This results in better low speed acceleration (take off, climb) but not speed.

In my opinion it is not neccessary or possibly not even a good idea (for other reasons) to match the total displacement to the comparable single engine aircraft.


John