Dont see the problem with the screw running down the centre, all it would mean is you have 2 sides separated by a tunnel for the screw.
Personally I would also keep the cast frame as it is already made up with the screw mounts etc, unless of course there is something wrong with it.
Edit, disregard the above comment, I have just looked at your other thread and see now the nut is connected to a central bar.