Otherwise you can weld the brackets to the underside of the roof, or probably a good metal-bonding epoxy like Superglue (but better ) should do.
Try "DEVCON" - this stuff is awesome, and VERY strong, it can be drilled and tapped and bolted to.
Just make sure the surfaces are spotlessly clean (use sanpaper etc & carby cleaner) mix the epoxy and apply it, prop it up and leave it in the sun for a day, and it will be as good as welding.
I know on 80's LTD's the rear drains always used to block, and one car had a swimming pool within the vinyl hood lining, the drains go down the rear pilllars to the wheel arch area. You should be able to just grab some clear hose from a hardware and run new drains through. Location isnt that important, as long as flow is all downhill from the sunroof and they drain externally to the car.