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Chelli had been set to challenge for the Commonwealth super-middleweight title, but champion Heffron had to pull out with injury, and Jeffers has stepped in as a replacement, while light-heavyweight Whittaker faces Vladimir Belujsky.
Jeffers, who is undefeated in 15 fights, should provide another dangerous challenge for Chelli, who boosted his reputation with a dominant points win over Anthony Sims Jr in February.
Whittaker, who demolished Jordan Grant in May, takes on Ireland-based Belujsky, a durable campaigner who has three times as many KO wins on his record as Whittaker has bouts.
In the main event, Savannah Marshall challenges heavy-handed Franchon Crews-Dezurn for the undisputed super-middleweight titles.
On an exciting undercard, Natasha Jonas can also become a two-weight world champion when she battles Kandi Wyatt for the IBF welterweight belt, and Callum Simpson can display his explosive power against Boris Crighton.
“Mark Jeffers is dangerous and talented," said Ben Shalom, BOXXER founder and CEO.
"He will be stepping up to a huge opportunity to fight Zak Chelli after Mark Heffron pulled out via injury. I’m delighted to turn around such a great fight - possibly fight of the night - in a matter of days. Credit has to go to both guys for taking on such a big challenge.