3 and four point harnesses in 197's

[Lammie]

Hi has anyone fitted a 3 or 4 point harness in a 197 whilst keeping all the interior? Its just i've seen the hook attached to the rear bench and can only guess that its for a harness setup? if so where do the side harnesses attach too?

hope someone can help!? Quite fancy a cheeky racing setup now and again!