Longmuir delivered his plea following a Hampden summit of 30 lower-league clubs – including Rangers – to plot a way forward for league reconstruction.
He said: "The mood for change is strong within the SFL and the mood for the SFL to take assertive leadership is also something the clubs are supportive of. The key issue and challenge will be to engage, persuade the SPL and SFA to help us deliver this as we believe it's right for the game."
The purpose of the meeting was partly to rubber-stamp a proposal for a three-tier structure based upon a 16-team Premier Division, a 10-team Championship, a 16-team First Division, and a full-blown SFL and SPL merger.
It also included play-offs between all the leagues, a revamped League Cup, a play-off at the bottom of the First Division to link up with a new pyramid structure, but no Old Firm 'colt' teams.
The new structure could yet be in place for the summer of 2014. It will be presented to the SFA's professional game board at the end of the month.
Top-flight chairmen will discuss the matter today, but SportTimes understands the only mechanism by which it could be delivered would be if 11 of the 12 top clubs voted effectively to disband the SPL or if the rump of the top-flight clubs were prepared to resign from the SPL – a process which takes two years to complete.