Unfortunately, I think you will find it is not quite that simple !
The middle seats in a 7 seater sit on four rails, shared with the rear seats.
The eight seater uses 5 rails !
So you will need the rails and the runners as well.
Since the rails are in different places you are likely to need new carpets and sound deadening materials too
I guess, as the sound deadening is out of sight, the original parts can probably be made to fit.
Nevertheless, it would not be a huge job, assuming the bolt holes and captive nuts are already in place under the chassis.
I assume you want the middle seats to swivel ?