Didn't Bob Rock spend over 3 months getting the guitar sound right? They triple a lot of guitar riffs in metal, maybe that would make it sound bigger? I know he spent 1 year just on the drum sound alone, hence why the black album sounds so flawless.
Anyhow, as ever a great clip hunter, you've nailed the riff, the tone is close to the original, however i think more volume is needed and a bit more mid, esp low mid, as you say more air.