Now Jenkins - a world record 1,090 Test points - and Leonard - a world record 118 international appearances - will return to play for Quinnell and pay tribute to former Wales captains and stars Quinnell and Howley.
"Rob said his team is strong enough to take on and beat most international sides - but I think they are going to have their work cut out against my side," said Quinnell. "Not only have I got Jenks' deadly boot, the bulk of Jason and some 14 British and Irish Lions, but I also have the secret weapon of Ally McCoist on the bench to unleash when the time is right."
McCoist, who scored 19 goals in 61 appearances for Scotland between 1986 and 1998, is now a captain on TV show 'A Question of Sport' and Howley said: "He has a burning ambition to play a game of rugby - and to play at the Millennium Stadium. When I asked him if he would take some conversions, he asked whether I wanted him to take them with his right or left foot!"
While the extent of McCoist's rugby talents remain to be seen, the former soccer star will be rubbing shoulders with some of the greatest rugby names of modern times.
"I have got some tremendous finishers and highly gifted players behind the scrum - a back three of Mark Van Gisbergen, Dafydd James and Kenny Logan with Allan Bateman and Gregor Townsend in the centre - is about as good as you can get," added 52-times capped Quinnell. "Lions pair Jenks and Kyran Bracken will call the shots from half back behind a pack bristling with experience. And who would want to pack down against a front row consisting of Jason, Mark Regan and David Young?
"There has been a fantastic response from the players and I am sure we are in for a thoroughly entertaining contest on Saturday."
On a special day for the Quinnell family, Scott's brothers Craig and Gavin are set to come off the bench and join their elder brother in a side coached by their father and former Wales and Lions legend Derek Quinnell.
BRITAIN & IRELAND XV
Mark Van Gisbergen (London Wasps)
Dafydd James (Wales and Lions)
Allan Bateman (Wales and Lions)
Gregor Townsend (Scotland and Lions)
Kenny Logan (Scotland)
Neil Jenkins (Wales and Lions)
Kyran Bracken (England and Lions)
Jason Leonard (England and Lions)
Mark Regan (England and Lions)
David Young (Wales and Lions)
Mick Galwey (Ireland and Lions)
Doddie Weir (Scotland and Lions)
Tony Diprose (England and Lions)
Paul Volley (England)
Scott Quinnell (Wales and Lions)
John Davies (Wales)
John Humphries (Wales)
Craig Quinnell (Wales)
Darren Morris (Wales and Lions)
Alex King (England)
Gareth Llewellyn (Wales)
Chris Wyatt (Wales)
Ally McCoist (Scotland)
Gavin Quinnell (Llanelli Scarlets)
Gavin Thomas (Wales)
Paul John (Wales)
Garan Evans (Wales)
Tom Smith (Scotland and Lions)
Tickets for the 'Tribute to the Legends' Britain & Ireland XV v Rest of the World XV are £10 and £15 for adults, half price for concessions and £19 for a family ticket (2 adults/2 children). There will be two curtain raisers before the main event featuring Rob Howley's former school, Brynteg Under 15s against a Llanelli Schoolboys XV and a Bridgend Past & Present XV against a Llanelli Past & Present XV.
Gates open at 12.15 pm with the first game kicking-off at 12.30pm.
Tickets can be bought over the phone at Ticketmaster - 08705 582 582 - on line at www.ticketmaster.co.uk or by calling into the Millennium Stadium shop in St Mary Street, Cardiff.