I too went with the crossmember that goes all the way across. For two reasons actually. One was that it's so much easier to locate the motor, and it helps to have it bolted on rather than welded on, because once you have the engine between the frame rails, you need to be able to slide it straight back to engage the transmission's input shaft into the clutch. The other reason is to add frame stiffness.
And being a bolt-in deal, if you ever DO need to pull your oil pan for some reason, you simply support the engine, unbolt the crossmember, and drop your pan.
If you knew how tight it is in there, you wouldn't want a weld-in deal. The frame rails are really too close and that causes problems.
