If it helps, I sold my double seat to a T5 owner who wanted to refresh his (former) builders van cab. He told me he was sure the fittings were the same as his double-seat thus was happy to buy it.
However, as you’re going from single to double.. you need to consider the passenger airbag; a van built with two captains seats most likely has airbags installed for such occupants, whilst vans built with the double-seat have a wider airbag installed in the dash to cover both front passengers.
If you’re keen on doing the conversion, there will likely be a queue of people that want to snap up your passenger captains seat. So you could see if they’re willing to swap airbags, too, to save you the expense.
A new bag would obviously be the better option, but isn’t likely to be cheap.
Food for thought.