I'm not sure if Vit seats will fit, the standard Sierra ones are a very snug fit between the wheel tubs.
Obviously you'll need belts - easy enough.
You'll need all the brackets too. Do you still have them? There is one centre bracket that both seats clamp onto on the back.
Then each seat has two L-shaped bracket on the front.
http://www.auszookers.com/index.php?nam ... pic&t=1675
I had to fabricate some, because I couldn't find any second hand.
It would be way easier to just buy some second hand Sierra seats with all brackets included.