Newbi here, have a 70 cutlass, planning LS1 swap ~450hp.
Currently stock motor with 2004r, rear end with 12 bolt cover. 10 bolt diff.
Wants posi and change gear ratio (~2.5 now i think, way under powered)

Where can I buy a posi diff and the gear set?
Don't want to replace with 9" ford, because I already have disc brake conversion and full boxed suspension kit installed =(

Thanks for any advise guys!

 

Welcome 70Cut!
I'm not sure I can answer your question but can share a bit of experience. I ran a 3.73 ratio with my 2004R and it worked out great with 275/60-15's on the back. About 2200 rpm at 60-65.

There's great people here....share some pics of your car.
V/R

 

507olds and monzaz on this site may also be able to help you with a posi and gears for your O-Type 12 bolt (they specialize in this stuff). SuperCars Unlimited also carries posi carriers but I don't know if they can get gears any more since most of the aftermarket companies (Richmond Gear,etc) quit making them a while back.

Another option is to swap the O-Type for an 8.5" 10 bolt rear with posi and gear ratio you want - it will fit right in using the same control arms and springs, just need a slightly different length drive shaft.