If we assume the situation is something like "I have this RHD G and the bulkhead area is rusted out.  I'd like to change the body out wholesale, but I can't find a suitable RHD body to switch to.  I DID find a LHD body and was wondering waht would be in volved with trying to replace my RHD body shell using this LHD one."

You're correct that the "dog house" itself starts out NOT drive-side specific.  It only becomes so when they choose which side to weld the battery box into.  Even the pedal box is a bolt-in piece.  So if you want to do the conversion, you'll need to carefully remove the battery box from your old dog house being careful to preserve the entirety of the battery box sheet metal and then do the same, sort of in reverse on the LHD shell, you'll need to remove that battery tray being careful to leave ALL of the body sheet metal intact.  I think there might also be some parts such as bracing for the stering column, etc that would need to be moved over.  I'ts been a long time since I had the parts truck torn down to that level.

The real PITA is going to be transferring ALL of the parts from your car into the new shell.  There is a world of minutia there.  Honestly, I might think about just buying another G.

It's funny I say this because I've actually been entertaining the idea of a COMPLETE body restoration in the form of a place that takes your old body, acid dips it to remove all the old seam sealer, rust, etc.  Repairs any rust, replaces the body sealers, and then performs a zinc phosphate and primer dip on all the body parts, just like modern auto assembly plants did before they moved to pre-plated steel.  The tough part is that in order to get it done for any reasonable ammount of money, I'd have to disassemble every component off the body myself, deliver the metal-only body shell parts to the place, pick them up later, and re-build the whole car.  A daunting task and unforunately for me after disassembling the parts truck I had, I know exactly what I'd be getting into so I can't even claim ignorant bliss.

It would be a heck of a nice thing to do though, turn the clock back 27 years on the body of my G, and bring it's rust resistant properties up to todays modern standards.

Ah, one can dream.... 

-Dave G.