I started this type of sports with dropping an outboard in the water, letting it rot for half a year and then, without any exprience, repairing it.
So: no guts no glory.
Assuming the engine of the 350 is similar to the 600, it is not as difficult as it looks.
Before removing the engine from the frame, make sure to loosen the big nuts on crankshaft, balancer shaft (have one), clutch and flywheel.
Crankcase splitter: never heard of such a device, always split my cases with some well aimed blows with the rubber mallet.
Removing crankshaft: could be done also by just inserting two bolts in the pretapped holes in left hand case (at least, that's the 600). To install: warm up the case in warm water, and put the crankshaft in the freezer for one night. It'll flip in easily. To remove / install the bearings, go to machineshop with a press.
While you're in there, replacement of all bearings, O-rings and seals is a good idea. Other items, as needed. Give special attention to conrod / bigend.

Now, most importantly: always keep using your brain; keep using your Clymer, and check, check and recheck. An before forcig something, first think!
And work clean.
And for Yamaha's: if it does not fit, it is installed in the wrong way, do not force it but stop and think!

The above, combined with some luck should see you through fine.

Auke

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Auke
http://aukemarieke.blogspot.com