The bonnet is a weird one, it's 70mm. If you order one from fleabay just make sure it comes with the lugs to screw it on. Much better than sticking it with silicone. And don't get sucked into buying a 73mm one - it will fit, but will need fettled to do so. The boot is 82mm, same size as the side repeater badges, but the boot one has 2 wee lugs that slide into rubber gromits in the boot lid.
Having messed about with aftermarket ones before I'd just go to a dealer now. Mainly because it's just easy - it's definitely the more expensive choice though.