suspension tracks 13 are fabricated from steel stock into a j shape with the hook end including a rectangular tube 22 or an equivalent form to provide the horizontal roller support surface 23 the tracks 13 fig4 are secured to the underside surfaces 24 of a plurality of bracket assemblies 26 spaced along the header designated 27 fig1 of the opening 12 fig5 the bracket assemblies 26 fig4 can be identical with the exception that the central bracket can have a double set of track mounting slots a main body 28 of the bracket assembly 26 can be made preferably of a single sheet of steel bent and welded into the illustrated shape the main body includes a vertical leg 31 and a horizontal leg 32 the lateral edges of the legs 31 32 are interconnected by triangular gussets 33 the top of the bracket 28 has a horizontal web 34 and a downwardly extending reinforcing flange 36 the web 34 is integral with the vertical leg 31 and the downwardly extending flange is integral with the web the web 34 and flange 36 preferably are welded at their lateral edges to the gussets 33 a boss 37 is welded or otherwise fixed at a hole 38 in the web 34 centered between the gussets and has a vertical internally threaded bore 39 a jacking screw 41 in the form of a threaded machine bolt is assembled in the threaded boss 37 a vertical slot 42 in the vertical bracket leg 31 is centered between the gussets 33 and a round hole 43 is formed through the vertical bracket leg on a common vertical center line with the slot thus preferably the slot 42 and hole 43.