Hey Ken,
then it looks good for the next step, checking perpendicularity of the router axis to different regions of wasteboard. You need some kind of swing arm that you insert into your router in place of a bit. This will allow you to measure the deviation from a right angle between router axis and worksurface.
Especially if you have a stronger pattern from surfacing bit on one side of the X travel than on the other side, it could be that your X rails are not on top of the other, and this more on one side.
Adjusting this is discussed here:
Do you have two longer rulers with a flat back, or two straightedges? You could attach them to the two X rails as described here, one at each end of X travel, and by looking from the side see if they are parallel.
This would mean using them as winding sticks.
If they are parallel, then the rails are on top of each other at both ends, check passed.
PS: Also what I would check on X rail is this (but you need to remove it from the machine it to check it, so I would check the other things first):