It was finalised after a marathon eight-hour meeting of top leaders of the two parties on Wednesday and an announcement is likely to be made in Patna on March 17, the sources said.
The Lalu Prasad-led Rashtriya Janata Dal is likely to contest around 20 seats, leaving the rest to smaller allies such as the party led by Jitan Ram Manjhi, RLSP of Upendra Kushwaha, Loktantrik Janata Dal of Arjun Rai and Sharad Yadav's party.
The RJD is yet to complete its seat-sharing talks with smaller allies and the Left parties.
The leaders had met at the residence of AICC general secretary K C Venugopal.
Four-time MLA Virender Chaudhary also joined the Congress in the presence of Gohil and the state Congress chief here.
"In joining the Congress, they have returned to their ideology. We welcome them in the Congress fold," Gohil told reporters after their joining.
The sources said efforts were also being made to bring back Pappu Yadav into the alliance, after differences had cropped up between him and his party RJD.
Asked about reports of differences emerging between the alliance partners of the grand alliance, the Congress in-charge denied any rift and said, "As RJD leader Tejashwi Yadav has said, it is a union of hearts and not just of parties. (dalon ka nahin, dilon ka gathbandhan hai)....There is no heartburn among the alliance partners."
He instead hit out at the alliance partners of the BJP saying even though they have decided on their seat-sharing, they are not announcing their candidates as the same is yet to be worked out and there are bickering within the NDA.
Gohil also denied that there was any proposal before it for leaving a seat or two for the BSP in Bihar's grand alliance.
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