Both players have dented the All Black lines on their home turf at Twickenham and on this tour, where England would have caused even more anxiety had they been more accurate around those sorts of forays.
For big men, Vunipola and Morgan have the ability to stay on their feet and get across the advantage line. If they can create enough repeat forays, those raids will take the energy out of the All Black defenders.
Vunipola will be a big bloke when he matures and fills out. He is 21 and in the apprentice stages of a test career which, if he dedicates himself, has a long way to go.
Remember Isitolo Maka, another No 8 with remarkable potential who played four tests with the All Blacks then fell off the radar.
He had a similar physique and in the form he showed around 1997-1999 was a potent part of the packs he played in.
Vunipola was born in Sydney, two years after brother Mako, who started life in Wellington and would have been on this trip but for injury.
Mother Singa is a Methodist preacher and dad Fe'ao played 32 times as a hooker for Tonga and represented the island nation at the 1995 and 1999 World Cups.
Religion and rugby moved the family to the UK in 1999, and they have been there since.
Both sons have reached the England ranks and if that progress continues will become another father and son combination, like their cousin Toby Faletau and his father Kuli, to play in World Cups.
Someone who has no doubt Billy Vunipola will graduate and make a strong impact is former England flanker Richard Hill, who claimed a World Cup winner's medal with the 2003 side. He likes the production England is getting from the Vunipola, Chris Robshaw, Tom Wood loose-forward partnership.
If Vunipola continued his conditioning work and developed his grasp on the international game, his bulk and power would offer an arrowhead for England to work with.
"England need their No8 providing that go-forward and that opportunity to get in behind the opposition defence, to allow the backs to play on the front foot, allow forwards to come around the corner without an organised defence in their way," Hill told the Daily Mail.
The Vunipola brothers flat together northwest of London and now play for Saracens, a situation they both prefer to the occasional confrontation they had when Billy was with the Wasps.
The No8 was in the England scrum for almost an hour last year when All Black rival Kieran Read showed out as the tourists rampaged to a 30-22 victory. Read ranged with great effect down the tramlines while Vunipola worked more down the middle of the field.
Their work will be at the core of tonight's match as they start this final test of England's tour, Vunipola after being on the bench last week and Read after time out because of concussion.
