if the finish is very very good and there is no damage/stone chips etc (unlikely) then just give it a grey scotchbrite, basecoat n laquer.
if its a not very good finish, ide wet flat the whole of the bonnet with P800/P1000 or P1200 until its totally dull and scotchbrite the inside.
if its got stonechips, depending on how many ide probably prep it with P240/P320, n primer anywhere i broke through the laquer.
but as said above, more than likely just need a nice wetflat all over, scotchbrite the inside and paint straight over it