The SPFL was finally given the go-ahead in the early hours of Friday morning after a deal was struck to reunite the two league bodies after 15 years apart.
But one of the first decisions the new six-man SPFL board will have to make is which of its two chief executives - former Scottish Premier League boss Doncaster and Longmuir, his counterpart from the old Scottish Football League - will lead the organisation.
Both men are running the new body together in the meantime but Doncaster remained cagey on his own chances of landing the post for himself.
He told Press Association Sport: "It's not a question of applying for the position. There are two acting chief executives and the board will be selecting one of those to take the new league body forward. Interviews will take place over the next 10 days or so but that's for the board to decide who they want to lead the organisation in future."
Longmuir, meanwhile, said he was keen to throw his hat in the ring, adding: "There will be a process over the next week or so where the newly appointed board of the SPFL will make a decision (on the new chief executive) and I will enter into that process wholeheartedly."
The new league body was due to be given the green light at a board meeting early on Thursday afternoon but wrangles over due diligence saw talks continue past midnight.
And Longmuir admitted he feared the long-running merger discussions - which have dragged on for the past four months and were almost sunk over plans for a 12-12-18 scheme - might collapse again at the 11th hour.
"There was a point in time yesterday where the SFL board were not completely satisfied to allow the decision to be made," said the former lower-league chief. "There was more time, more information, more co-operation required. Once we achieved that, it all began to develop.
"Should the information have been made available earlier? Well it wasn't for the lack of requesting it. It's all about communication in life. When we got to the point yesterday where we got the communication we were looking for, there was a momentum behind the decision and that was it."