Running a caliper across the top of mine, it looks as if my column top is 2.111" across, with 55-56 thou recesses to achieve the 2.00" arm gap. I'd think it's the 2.00" across the recess bottoms – with equal depth recesses – that you need to attend to, or several other dimensions'll be thrown out. But the thin flanges above and below the recesses only fit fresh air, so the height of those is not very significant.