I play in a sabbath tribute band and just use a precision with flats and for the distortion of the first two albums I use an Electroharmonix bigbass muff. I also use an ebs valvedrive to fatten up my signal before sending the bass to FOH. Look at your technique as well. Use your fingers instead of a pick between the end of the neck and p pickup. You'll get reasonably close this way. I don't think geezer ever used delay but I have a lot of fun using slight delay in black sabbath and planet caravan and it helps for the mood of the songs.
Proudly using Musicman basses, vintage ibanez copies, and custom builds.
Amps: Ampeg b15n + Acoustic 370
Cabs: mesa 1000 + Ampeg Heritage 410
I stomp on EBS, EHX, and MXR pedals.