The first thing that comes to mind is, why? 900 hours is nothing for those engines and unless they have problems they should last a long, long time. The boat was apparently designed for twin screws so I would think long and hard before I tore them out. There is an argument for simplifying things, but then again there is a good argument for redundancy. Have you actually operated the boat much, I'm wondering how much you would miss the ability to turn in it's own length versus typical sailboat handling which is generally pretty terrible? Just my initial thoughts without knowing any particulars.
SV Laurie Anne
1988 Brewer 40 Pilothouse