On the attached picture you can see my two "S" shaped gantries; each one is 1/2" thick, 4" wide by 26" high and I cut them from two pcs of aluminum each 8.25"x 26.25"x1/2" thick.

They turned out pretty good except in one gantry the straight part at the bottom only is 3-7/8" wide and the rest is 4" wide; the other one is 4" wide from the bottom to the top

All my alignments are done from the front edge of each gantry and so I don’t see any misalignment problems right now.

To compensate for the difference I was thinking when I home the machine one limit switch will stick out further by 1/8" than the other one

I could also screw on the edge of the smaller gantry a piece of 1/8" aluminum and then they will both be the same width

What is your opinion? 

If you design things (especially things like limit switch mounting) to be adjustable, it makes it possible to "Dial it in" to whatever position is needed to achieve as near perfect as is possible. It seems that no matter how precise the build, there are always those one or two things that just aren't quite right. Designing critical components to be adjustable with things like threaded jack screw holes, and/or slots for mounting bolts can make life much easier. (As opposed to disassembling, cutting, grinding, filing, sanding, etc.- which is usually the alternative when adjustability of the design is not utilized during the design phase). This important tid bit is usually learned at the School of Hard Knocks (experience).

Yes I do make the mounting of all limit switches adjustable so I should be ok.

Thanks for the reply