Howard 400

My partner's grandfather has just passed away at 101 and we have become the owners of a Howard 400 rotavator. The machine has been laid up for 20 odd years because the engine big end went. The engine was stripped down and just left, so is just a rusty lump now. The engine is a Kohler, but does anyone know if a Briggs and Straton engine would fit, as these seem more common than the kohler ones. The rest of the rotavator is like new and has the extra heavy duty tine bar for heavy ground as well as the usual L shapped feet bar.