Differential question open to a posi 1994 caprice

I would like to know what parts i would need in order to convert my current "open" differential to a posi/limited slip. Its a 94 caprice with the police package 8.5" ring gear. code gu4 for 3.08 gears. It does not have code g80 for the posi/limited slip. Also if anyone has converted one before if they could tell a difference off the line better/worse. And any performance related info handling etc. I dont have much experience with rear ends so any and all info is appreciated. Thanks

Have to replace the differential carrier, talking $500 in parts easy and really I would recommend more do gears while in there even just 3.42s are a nice step.
Even if you leave the existing 3.08s backlash has to be readjusted, taking playing with shims and a dial indicator. A shadetree mechanic can learn to do this but most guys prefer to pay.

Handling will depend on what sort of differential you buy, an Eaton will handle different than Torsen, Auburn like the stocker is discouraged because the clutches are not replacable like the Eaton and Torsen uses gears for torque bias so nothing to wear, shock loads can break them though.