First thing you have to do is WASH it down !! Sand gets blasted into the metal, so you need to get that out- I use rubbing alcahol because it's a lot cheaper than metal prep & the same thing.
Then you prime it with etch primer & block to find your lows & high's. Mud the lows- work down your putty & reprime with a good CATILIZED primer surfacer- block this down again to check for highs & lows, fix any that you find, and glaze any mud work with Iceing & sand & reprime with primer surfacer. 3 HEAVY coats & then crosscut this with 180 paper & then 320 paper. Wash it down with a good prep wash & seal it with a good CATILIZED sealer - 3 coats & let sit for a day to cure up. Wet sand this with 600 grit paper, wash, paint & clear. Cut, buff, glaze, and reassemble.
Piece of cake.......lol