Mercruiser 43-55778A-3 Upper Gear Set – 1.98:1 Genuine OEM Mercury-Mercruiser part. Fits:MCI, R, MR, Alpha One & Gen II (s/n 0K999999 and below) (19701997) 20-24 Teeth 1.98/1.94 & 2.40 Ratio .Special Order Item: This product is ordered specifically for your application. To help ensure proper fitment, please confirm compatibility with your engine model using our Parts Finder & Schematics Guide before placing your order. No returns or cancellations once processed.