....Which luggage rack is that? Is it the one that comes with a bolt on pillion?
This is a new replacement tank directly from Enfield, correct? If so, the reason the threads are "nasty" is because they don't plug them before they paint the tanks. Take one of the bolts to the hardware store and buy a threading tap of the correct size and chase the bolt holes. This should make things easier for you and not damage any threads.Scottie J