If you've got bare metal after blocking, its still not flat. Blast a couple more coats of high build primer and reblock. If you are any good with a hammer and dolly, drop the high spots back abit before repriming. If not, build the whole surface up good and reblock everythig to get it flat. IMO you should never leave anything bare and rely on sealer... It may sound like more work, but at this point, if you paint it, you'll more than likely see the high spots, and that'll ruin all you've done so far! Take the time to make it slick, you'll be so much happier in the end. Donny