Ok, so I'm installing a crank today.  I'm sure many of you have efficient ways of installing the crank and I would love to see the tools/methods, but today I found out Yamaha included a tool w/the bike!  No slip in for this crank.  Heating/Cooling does not necessarily offer enough thermal expansion in some cases.
This is one of them.    

Yes... a 14 Tooth installer...turns out the crank and drive splines/threads are the same.  During install, the gear did not not move, putting mostly downward pressure and no forward movement.  Thanks Yamaha. Very easy install.

Feel free to post what your favorite method/tools.   

Nice find!  Back in the 90's I saw a homemade dune buggy powered by a Yamaha two stroke.  The guy said the Yamaha transmission kept breaking so they gutted it and used a jackshaft with a snowmobile CVT belt drive.  The jackshaft was driven by a chain and sprocket off the right side of the crank.  I always thought they made a sprocket but they probably just used the stock Yamaha sprocket!  They used a modified handheld go kart starter to fire it up so if you stalled it, you were screwed.

I guess I'm lucky.  I've never had to pull the crank into the right side bearing.  Always has been a light slip fit and I can push in in by hand.

On the flywheel side I have a scrap piece of thick wall aluminum tubing that is about the same OD as the OD of the inner bearing race.  I made the puller bolt out of a tall flywheel nut and some metric all-thread I attach to the crank threads.  A couple of large flat washers go over the all thread and rest on the aluminum tube...  a nut is used on the all thread to pull the crank into place.  Easy-peasy.  

I cobbled my puller together years ago from scraps but if needed one now I'd probably just buy the set DEET sells.

I have seen good results using a cooler with dry ice and the wife's oven to install transmission and main bearings into engine cases in the past. 
I'd leave the dry ice in the bag you bought it. Put the dry ice in the bottom of the cooler and put a towel down to separate parts from the dry ice. Put the main bearings in cooler with the dry ice and the engine cases in the oven set to 200°. I just did this recently with a rosebud torch and dry ice installing new boom  bushings in an excavator. Worked a lot better than I thought it would. 
Move quickly and the bearings should drop right onto the cases. Let everything return to normal temp, then side cases back into the oven with installed bearings and crank into the cooler with the dry ice. Again things should slide right together. Only hang up I can see is if atmospheric humidity is high there is a chance of ice forming on the frozen parts or hot parts cooking off if you don't move quickly enough while installing. 

I'll be testing there theories in the next couple days as I need to replace the main bearings in my dt400 engine. 
My main concern is splitting the cases without hurting anything and no access to the fancy case splitting tool. 

Just use a two-bolt puller like a steering wheel puller to split the case.  Usually only needed on ignition side.   Auto parts chains often rent pullers for free, steering wheel puller sometimes works.

The right side case you're pulling on there actualy just slides in the crank if the bearing is in the case. That's if you already have the crank in the left side which is the tight one. Right is held over by the crank gear & nut. We all have our own methods & your one is another good one to remember. Thanks for posting--If i'm understanding the story correctly.