Colin,
As Eddie says, it does not matter. The voltages are so high, the spark will easily bridge any minute gaps (if there are any). Soldering does keep it neat and together, but if you do not have a soldering iron to do the task it is nothing to worry over. The gap at the spark plug sets the minimum resistance of the circuit. Once the potential is high enough to jump the gap there, it will bridge anywhere else of a lesser gap.
-Doug