Team captain Jack O'Donoghue has been ruled out of the play-off game as he continues to observe to the 'return to play' concussion protocols. His back row colleague Peadar Timmins will skipper Ireland in his absence.
The back row sees Timmins joined by openside flanker Rory Moloney with Frankie Taggart moving to number 8.
Dylan Donnellan and Oisin Heffernan will make their first starts of the tournament after impressing off the bench against England. They join Peter Dooley in the front row with Darragh Moloney named in the second row alongside Ross Moloney.
In the only change to the Irish back-line, Terenure College clubman Harrison Brewer will start in the centre alongside Junior Player of the Year nominee Garry Ringrose (voting details here).
Looking forward to his side's final fixture, Ruddock said: "Trying to defeat a New Zealand team at Eden Park is a formidable challenge for any Irish team but we will give it our best shot."
TG4 have confirmed that they will broadcast the 3rd/4th place play-off and the England v South Africa live from Auckland on Friday, with a highlights show on at 8.30pm that night.
IRELAND UNDER-20 Team & Replacements (v New Zealand Under-20s, 2014 IRB Junior World Championship - 3rd/4th Place Play-Off, Eden Park, Auckland, New Zealand, Friday, June 20, kick-off 5.05pm local time/6.05am Irish time):
15. Cian Kelleher (Lansdowne/Leinster)
14. Ciaran Gaffney (Galwegians/Connacht)
13. Garry Ringrose (UCD/Leinster)
12. Harrison Brewer (Terenure College/Leinster)
11. Alex Wootton (Garryowen/Munster)
10. Ross Byrne (UCD/Leinster)
9. Nick McCarthy (UCD/Leinster)
1. Peter Dooley (Lansdowne/Leinster)
2. Dylan Donnellan (UCD/Leinster)
3. Oisin Heffernan (Lansdowne/Leinster)
4. Darragh Moloney (Cork Constitution/Munster)
6. Peadar Timmins (UCD/Leinster) (capt)
7. Rory Moloney (Buccaneers/Connacht)
8. Frankie Taggart (Belfast Harlequins/Ulster)
16. Max Abbott (Cork Constitution/Munster)
17. Denis Coulson (Lansdowne/Leinster)
18. Rory Burke (Cork Constitution/Munster)
19. Stephen Gardiner (Lansdowne/Leinster)
20. Josh Murphy (UCD/Leinster)
21. Ryan Foley (Cork Constitution/Munster)
22. Conor McKeon (Lansdowne/Leinster)
23. Dan Goggin (Young Munster/Munster)
IRELAND - 2014 JWC RESULTS:
Monday, June 2: France 19 IRELAND 13, QBE Stadium, Auckland
Friday, June 6: Wales 21 IRELAND 35, ECOLight Stadium, Pukekohe
Tuesday, June 10: IRELAND 38 Fiji 0, QBE Stadium, Auckland
Sunday, June 15: England 42 IRELAND 15, QBE Stadium, Auckland
For the full fixtures list, please click here.