I'll check and see if I still have a set of the LeB-B instructions which I could scan for you. In the meantime, it is a pretty straightforward job if the wood underlying the perimeter of the opening in the top is free of rot and the wood bows are in good shape.
Apply a continuous bead of sealant all along the perimeter where the tacks will be, Follow that with the layer of chicken wire (available at Tractor Supply and elsewhere) trimmed short of touching the edges of the opening in the top. Then follow that with a layer of canvas tacked to the perimeter wood and trimmed. The second coat of sealant is applied covering the heads of the tacks. Next is a layer of padding is placed on the canvas, but short of the extreme perimeter of the trimmed canvas.
Next is the outer material tacked in place working from side to side to achieve a tight fit front to back, side to side, opposite corner to opposite corner. A second set of hands can make that part of the job easier.
After the outer fabric is tacked in place and carefully trimmed, apply another bead of sealant over the path of the tack heads and the edges of the trimmed material, finish the job with the re-installation of the restored original steel channel. I recommend that you use #2 or #3 flat top countersunk screws for that job unless you are a dead eye with a tack hammer. Better yet, use screws with Robertson heads and you will avoid scratches and paint chips on your roof or channel. Once the channel is installed, apply another bead of sealant in the channel thoroughly covering the screw heads to prevent the entry of water.
Lastly insert the rubber filler strip available from Dennis Carpenter, among others. What is available is not an accurate reproduction of the original insert, but it will do.
An hour or two in sunlight will stretch the top material and remove any puckers along the edges from your tacking.