oh btw: I agree Dan Huff's tone with GIANT was FEIRCE!!!
But to nail that Randy-tone (the studio version), I think the Plexi (or similar module) with a Boss Metal Zone (MT-2)in front should do it.
Essentially this does what a MXR distortion+, a 10 band EQ and some more EQ from the board did for him, back in the day.
To me, listening to Randy just shows how displaced he was. He was just doing the Ozzy band to get a head, seeings how Quiet Riot hadn't done much. And he basically grabbed whatever gear was available "off the shelf" to help him get close to what a new-metal (NWBHM, if you know the term) sound was like.
But he was really much,much more than a rock guitarist.
When I hear those old recordings I hear a guy bending over backwards to accomodate an ageing concept, an old form...and somehow blowing the lid off of it.
Well done, Randy....I STILL miss you.