that was the remains of the original roof cross member which was cut off for your pop top opening ....its probably been moved to the rear of your opening if its anythin like my Devon. The reamining bit in your pic will add a little bit of strength to the middle outer part of your roof. I'd leave it in place as the weight of the roof may cause some distortion/denting in that area without it IMO Originally, the surround to the pop top would have had some foam padding underneath the headliner which would 'pack out' the strengthener so it wouldnt be visible once the headlining is in place. I think you have a couple of options, either 1) pad out the top area down to the top of the window to cover the bracket with something like 1/4 inch foam and taper the ends a little so the transition to the window surrounds/sides is not noticed 2) cover the window surrounds with the same 1/4 inch foam all over so it is the same thickness all the way down to the door cards ...might give it the 'plush padded' feel/look or 3) cover around the windows by gluing headliner direct, pad out the top area only with 1/4 inch foam to cover the bracket, then cover the top foam padded section separatly making a neat fold at the bottom of this bit of headliner where it meets/overlaps the previous headliner you have fixed around the window opening......you would be left with a visible seam which would look fine if you do it neatly. you could always cover the 'seam' from option 3 or the 'transition' of the foam in option 1 with curtain rail
i think you may struggle to create a 'Flat' Headliner board, without being able to support it, unless you use fairly stiff composite....Hardboard will sag, unsupported...this is why Devons have a slight curve...the board is actually wider than the cut out, so it's held in place under tension. To achieve a flat head liner, you'll need some kind of cross bracing...this will need to be hung/ attached to the bracing already present, which is breaking out into a much bigger job. If I may be so bold as to make a suggestion. As most of the heat in a bus disappears thru the roof, why not use a piece of Kingspan (40 or 50mm) and vinyl it. This kills two birds with one stone, is easy to work with and super light (saving some weight). Reject sheets can be had for as little as £5....well worth considering from a practical, economical point of view, IMO
