Leicester Tigers prop Heyes, who has just agreed a new contract with the club, is named at tighthead in his fifth appearance at the Championship in Argentina while club colleague Reffell retains his place in the Welsh back row.
A third Tiger, Welsh fly-half Sam Costelow, misses out after suffering a facial injury in his side’s win over New Zealand in the last round.
Head coach Steve Bates has made three changes to the England team with James Kenny at loosehead prop, Tom Willis coming in at No8 and Luke James picked at inside centre.
Bates said: “This match is extremely important for us as a team, for personal pride and making sure we finish the tournament in a positive way.
“For the majority of the players, this will be their final game in the pathway and I hope they’ve all enjoyed the experience. I hope they will remember this experience very fondly and finish with a win.”
Wales head coach Gareth Williams has made seven changes to his team in Rosario. Injury to Max Llewellyn sees Deon Smith move into the centre with Tomi Lewis on the wing and Harri Morgan starts at half-back. Rhys Davies and Nick English come into the front row while Ed Scrag is at lock. Iestyn Rees has been rewarded with his form with a starting berth at blindside flanker.
"We have rotated the squad over the tournament, some of it has been forced on us because of injuries, but we are comfortable in changing our combinations," said Williams.
"Beating New Zealand is a massive part of these players’ development. The performance was far from perfect but the result was huge for this group of players."
England versus Wales is a 2.30pm kick-off (UK time) on Saturday, with live coverage on S4C and World Rugby platforms.
Former Tigers academy scrum-half Christophe Ridley has been named as an assistant referee for the World Under-20s Final between France and Australia on Saturday.
England Under-20s: 15 Tom de Glanville (Bath Rugby), 14 Ollie Sleightholme (Northampton Saints), 13 Fraser Dingwall (Northampton Saints)(c), 12 Luke James (Sale Sharks), 11 Josh Hodge (Newcastle Falcons), 10 Manu Vunipola (Saracens), 9 Sam Maunder (Exeter Chiefs); 1 James Kenny (Exeter Chiefs), 2 Will Capon (Bristol Bears), 3 Joe Heyes (Leicester Tigers), 4 Joel Kpoku (Saracens), 5 Alex Coles (Northampton Saints), 6 Ted Hill (Worcester Warriors), 7 Aaron Hinkley (Gloucester Rugby), 8 Tom Willis (Wasps Rugby)
Replacements: 16 Nic Dolly (Sale Sharks), 17 Olly Adkins (Gloucester Rugby), 18 Alfie Petch (Exeter Chiefs), 19 Kai Owen (Worcester Warriors), 20 Rusiate Tuima (Exeter Chiefs), 21 Richard Capstick (Exeter Chiefs), 22 Ollie Fox (Yorkshire Carnegie), 23 Tom Seabrook (Gloucester Rugby), 24 Ollie Hassell-Collins (London Irish), 25 Connor Doherty (Sale Sharks)
Wales Under-20s: 15 Ioan Davies (Cardiff Blues), 14 Tomi Lewis (Scarlets), 13 Deon Smith (Dragons), 12 Tiaan Thomas-Wheeler (Ospreys), 11 Ryan Conbeer (Scarlets), 10 Cai Evans (Ospreys), 9 Harri Morgan (Ospreys); 1 Rhys Davies (Ospreys), 2 Dewi Lake (Ospreys)(c), 3 Nick English (Bristol Bears), 4 Ed Scragg (Dragons), 5 Jac Price (Scarlets), 6 Iestyn Rees (Scarlets), 7 Tommy Reffell (Leicester Tigers), 8 Jac Morgan (Aberavon/Scarlets)
Replacements: Garin Lloyd (Ospreys), Kemsley Mathias (Scarlets), Ben Warren (Cardiff Blues), Morgan Jones (Scarlets), Lennon Greggains (Dragons), Dafydd Buckland (Dragons), Rio Dyer (Dragons), Tom Hoppe (Dragons), Teddy Williams (Cardiff Blues), Tom Devine (Dragons), Ioan R Davies (Cardiff Blues), Will Griffiths (Dragons)