Currently, Gary is using EMG's I believe an 81 in the bridge (I would be surpirsed if it was anything other than) and a 89 in the neck, and he's using them in all mahogany guitars. I don't know what he was using back in the day, but I would be surprised to find out that his guitars were anything but all mahogany. The SH-5 will sound very different in an alder guitar. Also, Gary's technique is going to be significantly different than what you play. You would have to get his exact picking, string gauge, and fingering style to get his tone. The SH-5 will get you close if you had the same amps he was using back during his SD period, but it won't get you all the way there. If you want a good thrash baseline that would allow you to play a lot of different things, then I would go with either the Distortion, the PATB- 2, or the Black Winter. Those will give you a tight, aggressive sound which will allow you to play the heavy palm muting required for thrash. I think the Custom is a little too loose for thrash.