Notes on the bidding:
1. The 2♦ is a new convention: Lee 2♦, promising one of the following hand patterns -
a) A natural 6 or 7-card ♦ suit, 6-11 HCP
b) 6-4 in the majors, 10-15 HCP
c) A big 4-4-4-1 hand, 16+ HCP
d) A big 5-5 holding in the minors, 14+ HCP
2. When North overcalled 3♣ East knew that West was either a) a natural ♦ pre-empt, or b) 6-4 in the majors. On both accounts East had good support for whichever hand pattern West had opened. So the X was obviously for takeout into whatever West held.
3. 4♥ was showing the 6-card suit
4. 5♣ showed a void in the suit inviting the slam if West's holding was doubleton ♣ and singleton ♦ in the minor suits. Reverse the minor suit holding and West would signoff in 5♥.
Now that you have bid the slam, you have to make it. Do you finesse for the ♥K or do you play to drop it?