A big part of jus osbornes sound on at least the first 2 albums is the boss Fz-2 on mode 2 with an overdrive after it (I think he used a boss sd-1) into big high headroom Amps.
The Fz-2 is a modern version of the univox superfuzz with an active eq (and a boost mode too)
I've got a north effects superfuzz clone with an ehx crayon after it and I can nail the tone on the first album (with a Tele into a super clean fender amp no less!!!)
The superfuzz severely scoops the mids at 1khz but the overdrive after it adds a bit of grit and puts some of the mids back in but at a slightly different frequency and also shaves off some of the fizz from the superfuzz.The lows with this setup are thunderous but tight.