Saftey is in the width. You decide the amount of saftey you want. Most kits are made with the economics involved so are bare minimum width and require you to purchase a positive offset wheel and this is fine as long as the body will take it and most dont.
56" is a good all round start for a kit and I would say that this would be fine width for a rear on a Honda or Harley. There is much more to it than I can write here but I think you get the Idea.
If you cannot find your center of gravity on the bike then you will be at the mercy of trial and error.
Just about every Honda or Harley we have had to fix had an 1.5 inch or more to the right out of X.
This is because of economics and profit. When this is true the Compression and Tension factors go out of site for the left side. Trike will run fine as normal use but when you hit that stick or bump in the road everything becomes abnormal and you will exceed the perimeters allowed for the frame strength itself and will become a cyclic stress failure over time(Out of warranty)
kodiak