If you are doing a body off full restoration, the gearbox and engine have to come out sometime.
I am on my 3rd bare chassis at the moment, and they were all separated with the engine and gearbox out.
It makes getting at all the cables you have to disconnect much easier. Also you can see down the tunnel as they are hopefully coming apart, to see what, if anything is left connected.
I always forget the cable from the handbrake horseshoe in the tunnel to the reaction lever.
I get down to complete bare shell, and complete bare chassis, so it all has to come apart at some time.
Probably a matter of personal preference, but I lift the bodyshell up, and slide the chassis out on a wooden pallet trolley, and that is light and easy without the engine and gearbox mounted.
Then the bodyshell is unjacked on to another 4ft square pallet on castor wheels, and they are both easy to move about.