The couple would make about 9500 Romney ewe lambs available to shear.
At the event, three more stands would be available for the public to shear on.
All shearers taking part would give their wages to the "good cause", he said.
He expected about 600 people to attend the "fantastic" event in the woolshed, which was built in the early 1900s.
Event manager Jared Manihera, of Alexandra, said the event was great because everyone was there to support the four men "putting their bodies on the line".
"The more we shear the more we make."
The event would run for 32 hours, the four shearers doing a dozen two-hour runs, with breaks in between.
A similar event in 2020 raised money for West Otago farm manager Shaun Bradley, who was battling cancer at the time.
The 2020 event ran for 24 hours including breaks, across eight stands.
About 85 shearers and rousies in the woolshed hit a final tally of nearly 7300 sheep.
A highlight of the 2020 event was taking a moment to watch about 90 people working in the woolshed when the clock struck midnight, he said.
Wells, of Roxburgh, will return to shear for 24 hours.
Listen to Rowena Duncum interview Jared Manihera on The Country below:
The rural contractor considers shearing a hobby and said he was aware he was the only man taking on the challenge who did not work full time in the profession.
He had set a target of shearing about 1000 sheep.
He would focus on his target rather than compare himself to the more experienced shearers aiming for higher numbers.
"They'll be chasing tallies in their mind but I'll try and block that out and do my own thing."
He was taking part because he had family who had died from cancer and mates who had battled it, including Bradley.
At the 2020 event, he shore 930 sheep, which was a physically and mentally draining experience.
"I was shattered."
A reason for being exhausted was being given only 10 days' notice to prepare.
As he had more warning this time, he was practising shearing, running for fitness and eating healthy food.
The 1000-sheep target was realistic as he would be shearing for longer than in the first event.
He hoped he could shear more sheep but did not want to set the target too high and "blow out" trying to reach it.
"I want to be there at the end."