No, it really isn't that hard.
I successfully filed the tapers on mine. I didn't measure the taper, I just wung it. See if you can color the inside of the square hole with a sharpie or something like that, then put the crank on the spindle as far as it will go, then take it off again and look inside the hole. You should be able to see where the spindle touched the crank, because the ink will be rubbed away there. So file that area away and color it in with the sharpie. Repeat. Until you have the spindle going in half way, nothing is critical. But as you get closer to finishing, you have to be increasingly careful. Don't go too far. In the end you will have to tighten the crank bolts a lot to push the arms onto the spindle as far as possible, which will reshape your new tapers a little bit. Don't be afraid to tighten it some more after riding a few miles.
I didn't mean to imply that I knew what I was talking about. The ratio with which you should lend credence to rhm's advice to mine is: 44:1.
It is a beautiful crank. It would be cool if you could find a way to re-use it.