The later 240s, 740s and 940s (89/90-on) either have LH 2.4 or LH 3.4 and EZK-116 or Rex-Regina (leastwise in the North American market). These systems use a crank position sensor (CPS) located on top of the bell housing to sense the flywheel and determine rpm rather than using a Hall Effect sensor in the distributor as in the earlier ignition systems such as EZK-117.

Alignment of the screws in the elongated slots in the rear cam mounted distributor caps should not be critical; The timing is adaptive and decided by the ignition controller based on rpm and engine load. As others note, matching the original orientation of the screws in the slots or just using the mid-point should suffice. Note that only 700s and 900s could have these rear cam mounted distributors. 240s always had side mounted distributors driven off the intermediate shaft due to firewall clearance limitations. Those caps align to a fixed notch and are held by clips.

If there’s a special procedure that Volvo uses to more properly align the rear distributor caps that I don’t know about then hopefully someone will post. Not many of us still have timing lights and know how to use them, let alone a decent dwell tach. I can’t remember the last time I used mine, if they even still work.

Now as for the rear mounted distributors themselves, I vaguely recall they also have slots for the screws, but something in the back of my mind says that one screw was not in a slot. Either way, it never hurts to scratch a mark for the top screw before removal.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now