I dont think the flipper kit will have the double switch required.  What you need is one of these:

http://www.rtbb.com.au/catalog/product_info.php?cPath=44_158&products_id=2913&osCsid=65450b8f64501cd5d6a9c9ce3ef1909d

You can make them up yourself, but it can be tricky.

don't know if I have these on my game but I bought exactly a set of these for my space invaders, so got them coming if need be. BTW I did make a set for my SI out of spare bits and you're right not a simple thing to do. They work fine but that's why I bought a pair with this order. Thanks