I'm an expert at this - I couldn't figure out what was wrong with the bonnet catch on my cooper, I had these 2 wierd spacer things left over after I put everything together, turned out they were the missing piece of the catch puzzle (item 3 below) .... here's an exploded pic and how it fits together - this pic is looking at the whole assembly as if you're looking down at it from the front of the car. I went and pulled it off the deluxe I'm working on, so it's very grubby
Item 4 is the only part that's outside the body - note the green circle showing the sloped cutaway parts, they go towards the front, more aerodynamic....
Item 2 goes directly underneath, and the spacers (Item 3) go through the slotted holes, allowing it to slide from side to side
the bolts go through the spacers (item 3) and into the plate with the captive nuts (item 1) which goes inbetween item 2's main body and the bendy bit
I've pictured Item 1 upside down, to show which way the bit that sticks out goes - it goes on the passenger side, when assembled on the car, the nuts should be at the bottom
Finally, the spring (item 5 - shock!) goes in the little hole and on to the bonnet slam panel on the passenger side
enjoy!
(edit) the blue lines show where the bolts go, the purple line is supposed to show the bottom plate going into it's spot... the big black circled bit is supposed to be outside the car