And the former Wallabies World Cup winner is confident that combination will help Tonga do more than just scare their rivals in a stacked group at the tournament in France later this year.
Kefu has spent three months of this year abroad, assessing his stocks plying their trade in Japan and Europe.
"We're going to have a really good team, probably the best ever," he said.
The Pacific nation is one of the biggest winners of World Rugby's 2021 ruling that allowed international players who had not played for their country in three years to switch to the country of their birth, or the country of their parents' or grandparents' birth.
Former New Zealand World Cup winner Malakai Fekitoa, All Blacks fullback Charles Piutau and forward Vaea Fifita are all expected to be named in Kefu's squad.
Kefu this week confirmed former Wallabies winger or fullback Israel Folau, who debuted for Tonga last year, will be there too.
"It's been crazy, crazy," Kefu said of his preparations.
Tonga, ranked 15th in the world, have played in all but one World Cup since 1987 but never progressed out of the pool stages.
The 2019 Japan tournament was arguably their best campaign, with a win over the USA and two-point loss to France.
World No.1 Ireland, defending champions South Africa, the improved Scotland (No.5) and Romania (No.19) stand in their way this September-October.
"We're in a tough pool, but we'll throw all our eggs in one basket and aim up against Ireland," Kefu said.
"We can't play footy with them; they'll beat us every day of the week.
"So we need to come up with a bit of a plan and I think we've got one ... it's going to be good."
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