Crafters seem to be available with two heights of handrake handle. If yours is higher than the seat base then you will need to add a spacer under the swivel so it can clear the handbrake on its way around. Also if you do not have height adjustable seats you'll have to remove some of the plastic seat base trim.
The swivel can be made to work with a twin passenger seat. The trick is: remove the extra spacers on the central seats seat belt receiver so it sits as close as possible to the seat base box, then when you want to spin the drivers seat you just need to slide the passengers seat cushion forwards - again this frees up a little bit of extra room to play with.