@newt - thanks.
Like David did in his tutorial? just increase the start frame to access the tile?
I'd seen this but it imports them all as sprites and not tiledbackgrounds, which I thought might cause slowdown. Not only that, the size of the level is 3280x912 which means selecting and drawing this way is going to be a pain, but until there's a better way.......
If your vision so exceeds your ability, then look to something closer.