I think this is a fine variant, Twiggly. Fewer bonus feats and much more limited selection than the Fighter, but it has the greater skills and Will saves of the OA Samurai.
Though, what real penalties/limits are imposed with the alignment restriction? What do they suffer if they violate that alignment restriction at some point? The Samurai of Oriental Adventures has detailed drawbacks for it, and loses a class feature IIRC in the event that they dishonor themselves to the point of becoming nonlawful. They also have a code of conduct, which your variant doesn't seem to have. I think the alignment restriction is needed for sufficient balance, but I'd prefer it be "any lawful" rather than "any nonchaotic" for the sake of imposing sufficient restriction on behavior. Likewise I'd prefer a Code of Conduct attached to the class; it doesn't have to be extensive or anything, of course. Drunken debauchery, dishonesty, ignoring orders, etc. shouldn't be considered acceptable knightly behavior.