Remember that (although it's frequently the easiest way) a larger round hole does not track the actual path of the pushrod tube as it cycles.
The relief hole's actual shape has a length (on the crank axis) of the tube OD + safety margin, but the cross (left-right) axis is 2 holes this size joined by a relief that allows the full in-out swing of the rocker arm (not an ellipse, the sides are parallel). This will depend in part on your rocker ratio - high ratio rockers are commonly made by shortening the tappet (short) lever, which increases the sweep of the adjuster. If you're copying a known-to-be-safe similar engine, beware of cam & rocker differences.