I rigged mine for an 898 just like yours and in my opinion I would stay the same way you have them just replace the old SI ducer with the new MSI ducer.
If you switch them the MSI/SI ducer image will be obstructed by the high-speed ducer. Unless you are going to switch to an MSI ducer on each side of the hull that is (this would be a total of 3 ducers).