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I have been a certified crankshaft rebuild station since 1971, and over the years, have built fixtures to do the work, along with the metal plate and cylinder the factory first had.
All that said, to check alignment, I built a steel plate fixture with two slideable V blocks to support main bearings 2 and 5. The sliders allow for many different crank lengths, like S vs H series vs Yamaha, vs Suzuki, etc. I build the crank to each of the inner end flywheels, 2 and 5, and check and set the center rod pin to get the center alignment. I then add each end one at a time, still supporting my center aligned section, and set the ends as I install them, done. I support in the V's mains 2 and 5, then dial indicator mains 3 and 4 to align.
The one thing I never do is hit the crank with any sort of hammer, older versions of crank align "tech" used a lead hammer to whack the flywheels into alignment, but, now, I have more fixtures I built that hold the flywheel in my press, and press another flywheel into place to align.
I also built an indexing fixture to get the phasing dead on as I build the cranks. One of the first Yamaha racar cranks for a specific pressed together 4 cylinder race crank had 90 degree phasing, not 180 degrees, one of the very first "cross plane" builds. The tech on that was/is, a 90 degree 4 stroke V twin has great torque control, but, the cycling to get the engine back to the firing point is lengthy, with no firing in the off cycle. By building literally two V twins into one engine case, that fire TDC and 90, then 360 degrees later, so the same, gives a more manageable torque delivery, smoother operation and very much better performance. All this came about from other crankshaft phasing changes, like in the V4 two stroke race engines with changes from 180 degree firing, down to 90, 54 and 45 degree phasing.
All this is from someone that was there at the start of doing it, and one that is fanatic on building my own tools and fixtures for all sorts of things. Most people just don't have the ability, nor facilities to build those things, although they do have the mental ability to know there are ways to do it bad, good, better, and exceptionally, best. Those people need the people on this site that do offer their crankshaft building services, they get it done right.
Do I do crankshafts for others, well, not many, mostly for myself, and other racers that are still riding in local events. It isn't hard to get a crank dead straight, only have to have one that wasn't abused in a previous incorrect rebuild.
As John said above, find a crank person you like, and go forward with it.
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What I did with Charlie Smith...... 
