I think that bench was designed and made by Bo Peterson of Sweden and if my memory is correct the mould consists of 3 parts, if you look closely, you can see bolts at the front edge of the forward upright edge.
It also looks like it splits at the rear where the two tabs are on the back of the bench top and possibly the right hand edge of the rear of the vertical support, and the front part of the form looks to split on both sides and pull away.
Bo would be only to willing to give further details.
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