Thanks for that. They did come out the top - I had to unscrew the jet about halfway and tap it down to help it out then I got a bolt with the same thread to screw in which I used to tap it out the rest of the way. I couldnt get the washer out so I just tapped it all the way out with a small screwdriver and left the washer in place. This one was stiff all the way out.
The brass pins are to guide the jet holder (or needle jet) into the right place to line up the holes so that the petrol/gas can come through the main jet and also from there into the pilot jet in front which is corked with a rubber bung. You don't need to drill them out - they dont secure the jet holder, just guide it.
It was well worth taking the needle jet/main jet holder out to clean it as it has 12 little holes to progressively allow more fuel in as the needle lifts. They are easy to clean with a (sewing) needle or a pin and a bit of air and toothbrush!!!
BTW grusvag I would have thought that under the brass plug in your pics is a screw just like the other ones
Good luck everyone. Thanks for your help.
Tony