I ended up temporarily removing all of the galaticraft mods (galaticraft, galaticraft-planets, and micdoodle), loading the game, letting it bark about errors and delete all of the galaticraft blocks/tiles. Map loaded successfully and worked fine (shy of no GC).
Then I put the mods back in and booted back up.
Working nicely now.
I thought I had tried that before but must have missed getting all 3 of the mods out of there so the game could successfully boot.
Cheers,