Done!

Not as difficult as I thought.

This pic shows it (still not sure what it's called) off the seat with the leather off. It's made up from a sheet of steel/aluminium some plywood and foam. I had already put a bend back in the metal by this time.

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This shows the bolt holes on the side of the seat. Bolts are those star shaped size T25.

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I took the opportunity to stretch and glue the leather to take out some wrinkles before bolting back on.

Thanks all.