crack in water jacket crank case top

What made the crack? I would take it apart and see. Possible to weld the case from the crank side, but would be hard to weld as in the pics, never mind the contamination freeze, oil etc.

I think a good welder could close that up as is with out taking anything apart....if not stuff a small cloth down there...spray with brake clean..v notch as much as possible with a dermal...
then marine tex/marine epoxy or jb weld..

wet vac after for clean up..

assuming the pipe and can are already out, cylinders/carbs/clutch are apparently off? you will need to disconnect the following
pull the starter rope out and tie a slip knot in the rope so it wont retract
remove 4 recoil cover bolts, may be torx or hex head. The cover can just lay in the belly pan
disconnect the wiring
Remove coolant hoses at the motor after placing a large drip pan under the sled to catch coolant. do not reuse.
Scribe around motor mount washers for easier reinstall location. you will need to realign the clutches.
Remove 4- 16mm engine mount bolts and washers
Tip motor forward and hold in tipped position with a small block of wood. remove the oil pump circlip and washer (put in zip lock bag so not to lose it)
Remove main oil line from pump and tie up along resivore so as not to lose additional oil
Remove pulse line for fuel pump.



I think that should get it out.

I forgot to add

if you are going to split the case there are bolts and cap screws on both top/bottom and the recoil flange

You will also need a puller to remove the flywheel prior to splitting the case.