Interesting this came up, as I'm about to transfer mine to a new GRP bonnet so will be going through this again.
Just take your time and as said, measure and remeasure and remeasure again. I read somewhere that placing them on the outer edges where the bonnet raises behind the headlight area can distort the bonnet when it's locked down, so I tried to get them inside of the bonnet crease.
I found one pre-drilled hole for the first pin and measured for the location of the pin on the other side until I got two locations that worked. Probably want the pins fairly plumb straight too, I had to mess about afterward trying to get them angled correctly so they would enter the catches smoothly as the bonnet came down.
Then checked this location would work for the aero catch locations on the bonnet.
With pins fitted, small drop off the (steel) bonnet will mark the location, pilot drill these holes. Be aware of your drilling angles to ensure you keep it all aligned.
Tape on the templates/paper templates to the top of the bonnet where this hole dissects the expected pin entry holes. I used a permanent marker that bleed through to some masking tape i had already applied to the bonnet in that location - worked a treat and helps prevent slippage whilst cutting and drilling.
Take your time and cut as you see fit, I used a Dremel. Remember, it's easier to nibble away at the body work until you get a snug fit for the catch, not so easy to add it back :smile:
Don't drill holes that are too oversized for the catch screws, they're pretty tight to the edge of the cut so use the smallest size drill you can get away with.
I painted all the edges of the bare metal work to prevent rust.
The lock nuts that came with my pack where crap and rusted quickly, I shall be replacing these with some new s.steel ones. Smear some grease or something on them.
Tweak the height of the pins until the catches lock without being forced, oil the catches.
I used some cheap edging off of eBay to finish the cut edges.
Hope this helps a little.
Ian
Some pics....