"We'll let Kahl roll there. We can cover it," said coach Jason Hamlin.
Lock Matt Ashworth, who filled in for the absent Lane and Hay-Horton against the Evergreens, is available for the camp but not the Saturday game.
"We're replacing one to fit another," said Hamlin.
"I think we're pretty much round about [full numbers]."
Mumby's return is well-timed, as winger Jack O'Leary, who scored against the Evergreens, has been invited to join the NZ Marist Colts on their upcoming tour of games.
Big prop Keightley Watson has also been selected, however, as the former NZ Marist coach Hamlin used his connections to get permission for the young man to delay joining the Colts until after Saturday.
"It'll get the most out of him in terms of his progression."
Having Hughes back strengthens the loose forwards considerably, but Hamlin was still impressed with Regan Collier's outing at No7 against the Evergreens, so the openside flanker spot has not been locked in by anybody at this stage.
Hamlin hopes their time together in camp is where the squad will really start to gel and lift their intensity heading into next month's Bunnings Warehouse Heartland Championship.
"As coaches, we put [plans] all on the table for ourselves, and see where everyone falls within that.
"I guess the message to the boys on Tuesday night, as well as I thought they played, was 'there's still a lot of work to be done'.
"We've just got to get the pace of the game quicker."
With 2021's first-choice goal kicker Ethan Robinson still at least two weeks from recovery for his shoulder injury, skipper Dane Whale and first-five Brooke Tremayne will likely take a little time for some practice on Cooks, after no conversions were slotted against the Evergreens.
"If they don't, they'll find out pretty shortly where they should be," said Hamlin.
"Not having Craig [Clare] limits you, from where you were before."
As of Wednesday night, it is not known what the composition of the Taranaki Development XV will be, as their Taranaki NPC squad also has a preseason game with Wellington on Saturday.
It is likely at least a handful of the squad will be from the Tukapa and Clifton clubs, who fought out an epic TRU Premier club final at Vogeltown Park last weekend, with underdogs Tukapa pulling off a thrilling 22-21 win.
With several newcomers to the Whanganui lineup, Hamlin will be reminding them of the history of the Jones Brothers Shield, which is on the line.
In 2016, for the first time in over 20 years, the TRU resurrected the shield for games between Whanganui and their Development XV.
Previously, from 1981, the shield was on the line in Queen's Birthday Weekend games between Whanganui and the full Taranaki NPC side – a fixture that had left the calendar with the advent of professionalism.
Whanganui won the shield in 2016 and have traded it with Taranaki Development twice since, reclaiming it last year in Hāwera with a 53-5 victory.
"It's never nice to let those things slip away," said Hamlin.
Kickoff is 2.00pm.
