If you put a 60mm gauge in, it will not fit quite right, you will have to chop off a small amount, see this picture:
the bottom is flat, its' not round, so it will be hard to center a 60mm gauge. But the rest of the circle fits for 60mm, just the bottom flat part screws it up. I've since redone that, centered and mounted it better, no pics yet. also if you don't take it out of the gauge housing it will be even harder to fit without modifying. you could cut out that bottom flat part and contour it with a dremel to fit better.
later on i plan to get a full set of 60mm defi's and do a much better job.