EDIT:
Just re-read your post, and realized i missed the last sentence. Sorry.Post is still valid though if you want to run with the sedan body. It could be the new weight distribution, but i doubt it. It shouldnt make that much of a change, RCbodies are generally weighted (material volume wise) to be as balanced as possible... Still, check out these solutions...

If i'm reading you right, your problem is that the car doesnt transition quick enough, and you want your rear end to slide around quicker...

Some suggestions to get a "quicker rear" would be doing things that increase your steering response.

Try these in SMALL INCREMENTS, ONE AT A TIME!!!

Increase your steering angle as much as possible. This will help your car pull back from a bigger angle.

Change your front toe to either neutral, or toe out. This will make the car more "aggressive" as it turns, and thus turn quicker.

Increase front grip, a few ideas there:

Put more "weight" on the front by changing ride height. This will make your car press on that end a tad more, increasing its grip. do this by:
Lower the front height
Increase the rear height
Physically add weights on the front end (this will however increase the ACTUAL weight of the car, do this sparingly)

Try reducing the front camber, this will increase its contact patch, giving the wheel a tad more grip as more wheel is touching.

You could also increase rear camber, but this would result in a smaller contact patch, making the rear more "slippery", though not necessarily quicker.

My final suggestion if you still cant get it:

Use a front one way.

Front one ways accommodate a different driving style all together, and you might have to change how you drive significantly to use it. With it in, your car while ON POWER will act like a 4wd car. Off power, it will act as a RWD car. It gives your steering a VERY aggressive feel, and effictivly gives you E-breaks. Let me explain and hopefully you understand:

Front one ways work by only letting the wheels put power down in 1 direction. The result is, NEITHER wheel spins slower then the other, and thus you get a LOT more power up front into your turn. (Normally, with standard diff action, one wheel, the one with the most grip, will SLOW DOWN, while the other speeds up. This equalizes the traction between the two, but over all your experiencing a net loss in power between the wheels. Kinda hard to explain and i dont have the mental fortitude to sum it up in less then a 2 paragraph explanation of why they work)

Anyways... back to front one ways...
The final result is the car will be pulled through the turn. Since your wheels dont loose power when they slip, it will act VERY aggressive. When you break, the rear wheels will lock up, but the front will be allowed to spin freely, so your front wheels will still grip, letting you turn while your rear will slip out and try to pass the front.

The real kicker is, it allows you to tap the breaks, and throw the rear out. This is especially useful as it lets you "force" a drift angle when you otherwise wouldnt be able to break the rear loose. This lets you run a high grip setup with out loosing the ability to drift. This is also how i drive.

I personally like front one ways. I feel theyre ideal for technical tracks, and high grip drifting, as you can throw out your rear at will with minimal effort. They do however require a higher level of skill to keep from over throwing your rear however. If you enter a turn wrong, or too shallow, instead of slamming into the wall, you can tap the brake, and change your drift angle.

Well, thats my suggestion...

Sorry for the lengthy post, i'm too sleepy for simple explanations. Hope you understand, if not i'll try to clear it up when i'm actually awake...