It's actually easier to take the lines off otherwise you end up bending them around and if they are old/original like mine were they may be brittle, there are good videos/threads on removing the turbos available. It's a bit of a ball ache but can be done.
I ended up putting braided lines back on mine, but regret heavily not doing exhaust manifolds and dump pipes. So if you are getting elbow deep into GTR turbo's I'd suggest going in with a plan and parts. All gaskets, new turbo's, exhaust manifolds with studs and metal gaskets, braided line kit or new lines, dump pipes of good quality and new oil drain hoses.
You could get all the mech parts second hand as most people just go single turbo so there are heaps of Turbo/dump/manifolds available with low mileage to save cash.