North has only 1 entry, only check the Spades not the diamonds. If you had no entry the proper play is A and low for 2 losers when its 3-3 or when either opponents have Hx (note that its also the proper play when you aim for exactly 3 tricks). Going to dummy and play low S to the J gain when East has both honnors & at least 3 card.(KQx or longer). The profit form going to dummy to play a spades is very low and imo rarely the best play when you have only one dummy entry.
(check only the diamonds) your in a suit contract and D is a side suit but since you dont want to touch another suit its time to attack the diamonds. You think the honnors are split because of the bidding & because either defender holding AK or AKx would probably have lead it at one point. If you need to make 2 tricks you have to guess who has Hx. If you think east is short you can go to dummy and play low to jack planning to duck all around on round 2 this win when East has Hx or HH(x). However starting the J from you hand and ducking round 2 if west cover is basically achieving the same goal but without wasting an entry.
Do you have some examples of those suits combo ? Are they frequent or are they rare ?