Tried 13cms - too big swapped them for 10cms too small any suggestions.

Might have to make a pod for the 10s.

The standard speakers were a single cone, no sign of a tweeter anywhere so no wonder the back sounded pants

 

5" will fit in there with a small (6mm) MDF ring . You don't need to worry too much about depth because the window doesn't go down far enough to hit the speaker.

Cheers,
Nick.

 

Thanks Nick