Full-backs James Bree and George Smith are back in the reckoning alongside forward Marley Watkins.
Bree has been out since mid-April with a hamstring issue following a recurrence of an old problem.
Smith has been sidelined since mid-March with a similar hamstring injury, with his last game coming in the 2-0 home loss to Southend on March 12.
Watkins, who has fired eight goals this term, is back after recovering from a broken jaw sustained in the game with Oldham Athletic on April 12.
The only absentee is winger Ryan Williams, who has made just one appearance all season due to a long-standing groin issue.
Barnsley have named the same starting line-up for the past five matches.
Heckingbottom said: “It is funny that the last time we had everyone fit was at Wembley and we have got them all fit again this week. Mad isn’t it..’
Meanwhile, Millwall’s Yorkshire-born defender Byron Webster is a doubt for Sunday after limping off with a hamstring strain in last Friday’s semi-final second leg at home to Bradford City.
The former Doncaster Rovers centre-half, 29 - from Sherburn-in-Elmet - has formed a formidable central-defensive partnership with fellow Yorkshireman Mark Beevers, with the Lions conceding just two goals in their last nine fixtures at The Den this season.
Manager Neil Harris said: “Byron came off with a strained hamstring, so it’s not ideal preparation because he has been colossal for us in recent weeks and months.
“It’s going to be tough for him for Sunday and we’ll give him every opportunity to make it.
“But if not then in Tony Craig, our club captain, and Sid Nelson, who has played really well this year, I’ve got players who can step into the position admirably.”