The Broncos will travel to Leigh Sports Village as massive underdogs, looking to reach Wembley for the second time in their history.
They will be boosted by the presence of Soward, who missed last week’s defeat at Widnes and who led St George-Illawarra Dragons to victory against Wigan in the 2011 World Club Challenge.
The Australian joined the Broncos on a short-term deal from the Dragons last month, ahead of a close season switch to Penrith Panthers.
Rea said: “We’ve got a few 50-50’s at the moment so we need some blokes to pass some fitness tests tomorrow, before we can even think about picking our team.
“It’s just begun, we’ve had a think about how we want to approach the week and we’ve discussed that, we’ve had a brief chat about how we want to play.”
London featured in the 1999 Challenge Cup final, when they went down 52-16 to Leeds, having defeated Castleford in the semi-finals.
Steele Retchless won the semi-final with a last minute try, and Rea was chief executive of the club at the time.
He said: “It was a great experience. It was a long time ago so trying to remember it is hard. You can see that you’re still talking about it and people are still asking about it. So that in itself says to the players that’s the sort of legacy you leave. That’s the opportunity you’ve been given.”