This thread has inspired me to fit some locating pins.

The holes are already in the body and bonnet
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Put the bonnet on and got it where I wanted and used a bent sharpened nail to Mark some masking tape to check for hole alignment.
A bit of fettling was required to get them lined up.
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Used the tips from some old braising nozzles I had lying around. Drilled the hole larger and used a wood screw to fix them into the ash frame which is under the hole in the body.
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Keeps the bonnet in place now, all I need is some new helicopter tape👍🏼