Steve
No sure if you have the Marlin build CD but I have shown on this post the Fickle finger of fate akc the hand of Mark and the role cage and window screen positioning if it helps.
You my notice to the left (towards the rear of the car) of the bar the removal of the bracket that is/was welded on to the top rail. I found after a lot of head scratching
that I needed to remove this bracket as well to make it all fit better.
I have also shown a picture of the rear mounting and the spacer I fitted.
The engineering never stops or it would be a jigsaw.
JohnC