I broke the back of one of my E15s a few years back hauling a boiler out
of a neighbors basement. I limped it home, (my bother and I stood on the
deck to maintain drive belt tension!) loosened the drive belts,
straightened it up, wirebrushed (and kissed it with the angle grinder in
a few places) and welded some 1" angle steel along the lower edge of
both sides... not a continuous bead, but just a nice connection every 3"
or so. Then applied some lovely rusty metal primer, snugged the belts
back up, and got back to work.
The top of the tractor deck is likely strong enough... all you have to
do is beef up the lower edges of that same stamped part... a few holes
in the vertical surface, or even scallops out of the bottom edge, won't
matter with fresh steel in place. Good for another 40 years.