Surely it's obvious that 4 are Belle Vue, King's Lynn, Leicester and Sheffield. Then the fifth is either Ipswich or the mystery Northampton/NorthamptonatOxford/Peterborough new team.
Since Chris Louis wanted 6 teams and refused to compete in a 5-team league, maybe the addition of a 5th team, will encourage him to return and make Ipswich a 6th team?