cross-section of a beam of the mounting assembly; FIG. 7 is a perspective view of a shoeof the mounting assembly; I FIG. 8 is an underneath plan view of the shoe; FIG. 9 is a section taken on line IXIX of FIG. 8; FIGS. 10 and 11 are perspective views of modified forms of supports in the mounting assembly; and FIG. 12 is an exploded perspective view of a modified form of cradle for use in the moun