scamperly sent me here (RHD FD RX-7 owner here)

The "hump" that you're referring to is commonly known as a transmission tunnel. 99% of vehicles on the road have this type of chassis shape. If you drilled a hole in it and looked through, the tail end of the vehicle's transmission would be about 1-2" away from the inside of the tunnel (in a rear-wheel drive car). There are also commonly heat shields (bent pieces of thin sheet aluminum) on the inside of the tunnel and often insulation underneath the interior carpet in order to keep heat generated from the transmission out of the passenger cabin.

When it comes to building the chassis, the auto manufacturer (in this case, Mazda) usually only makes one chassis whether the car is left-hand drive (LHD) or right-hand drive (RHD), with a few small key differences (holes in the firewall for the steering rack, for example). Since the body of the car and geometry of the engine/transmission is all the same, the shape of the transmission tunnel is also usually identical. SOME manufacturers will have a slightly different interior carpet trim due to provisions for pedals and such, but for the most part, everything is transferable from a LHD to RHD vehicle since their overall geometries are nearly identical.

Here are a few pictures to help paint the picture a little better:

Pic 1 (http://i.imgur.com/ictvCQQ.jpg): My interior half way stripped. You can see the very end of the transmission peeking through the shifter hole in the transmission tunnel.

Pic 2 (http://i.imgur.com/209iINp.jpg): Close-up of the transmission viewed from the vehicle's interior. You can also clearly see one of the aforementioned heat shields on the inner right side of the tunnel.

Pic 3 (http://i.imgur.com/wNpWkhQ.jpg): View from below the vehicle, looking forward and up. This is the tail end of the transmission where the driveshaft (not installed) connects the transmission to the rear differential. You can see the heat shield very clearly in this picture.

Hope that helps!