Proof that these gearcases are not considered robust / strong.------Fairly common for those to break.-----Surely there must be other damage here.----Bearings full of metal bits ?
What type of boat and usage.. Will not hold up under a heavy boat ,toon or tube/sking...PM me for gear replacement info....all gears and dog $219 OEM list over $1000
You need a " special " tool.----Suggested in the manual I have.-----7.1 mm diameter.-----75 mm long----and a 20 degree angle ground on one end to go about 1.5 cm up the side..----So step # 1 is to make the tool.
I believe you should take the propshaft / shift plunger apart.------In my humble opinion you could then see what you need to make.---Sorry.-----I have a few of these with clutch dogs that need to come off.-----Not hard to make this tool !!