Does the engine need to come out of the bay to gain access? Yes, unless you pull the head off.
Does the head need to be removed from block? Only if the engine is still in the car.
Does the head need any type of drilling/machining/welding for provision to attach the drain fitting(s)? Yes, knock out the welch plug then drill and tap two holes.
Does the sump need to be seperated from the block? No but if you pulled out the engine you possibly would to plumb it into sump.
Does the sump need any type of drilling/machining/welding for provision to attach the drain fitting(s)? As per above, only if you remove engine.
The biggest part is removing the engine. Personally I would remove the engine and coincide it with other bits and pieces to make it worthwile.