Looking back at my build log it's not entirely clear. Just says I aligned things the best I could by eye. You just want a few plumb bombs and tri-squares to help you get things close to center as possible. I think there are some posts by Dan Horton in the archives on this that are worth looking at.
This is the time you want to think hard about the bigger tires, if you are ever planning on operating off grass or gravel. I had to go back later and re-trim my wheels again. If you do go down the path of 380-150x5 tires, they are and inch wider and an inch larger in diameter, so you just use a 1/2" spacer block on the top instead of the 1" specified. They fit so well it's almost like the wheel pants were made for them. If you are only operating off sealed airfields, then stick with the smaller tires, as these larger ones are more expensive to replace, however this is not an issue on grass as the tires essentially never wear out. Mine came out great, and very glad I did it as 90% of my operations are off grass or gravel. There will be a 3lb weight penalty however (1.5lb each tire). You can re-use the same tubes.
Tom.