If you're going to bugger up your AWD suby (temporarily) by going RWD then you might as well chuck in a welded R160 rear diff. Maximum fun then, 100% locked at all times Just grab a cheap open R160 of any ratio at all, get somebody to weld it up and you're set!
I drove an RX-7 with a welded rear diff for years. Makes the car incredibly tail happy but also incredibly predictable once you are used to it. No snapping back into line unexpectedly, you know exactly how it's going to react because it's welded, nothing changes, just the wheels either spinning or gripping
More chance of busting stub axels or driveshafts or CV's though of course. Also makes parking a bitch. It's not for pussies.