e-bay my friend, ebay.

That savage backrest is S-O-L-I-D!

...a P in the A just to drill through, find a
slightly wider one (used, whatever) and
make a double-decker; 2 nuts & bolts per
side and make a black vinyl cover for it.

Trust me, it`ll hold.

...OR what if you just extend the cushion upwards
with a longer rear metal plate, new foam and new
lether/vynil covering?

Good luck and either way pls show us the finished mod!