Car seat confusion! help!!

[AliceMap]

Hi all, I've searched and searched but can't quite find the answer.
I am hoping to purchase a bongo with a rear facing back seat (was once front facing but has been turned to fit the kitchen bit at the back)
This means it is away from its seat belts.
Is it possible to fit a front facing 5 point harness child car seat to the central rear facing seat with a the lap belt??
By all accounts rear facing bongo seats are safer but lap belts are not.
So my child would be in the middle seat facing the rear but in a front facing seat....
if so does anyone know a suitable child seat that would fit with the lap belt.
confusing!!
Thanks,

[Hazzobongo]

Apparently rear facing seats don't need to have seatbelts at all and the reason the previous owner will have turned this one will probably be to make the entirety of the rear into a double bed which is what I plan on doing to mine so unless you are going to refit the seat in its original orientation facing front your access to the belts is gone.

I'm unsure as to the harness as I've had no kids since 96 and never really had to bolt my kids down in other cars/trucks and just used what was fitted but nothing is impossible for a decent handyman to figure something out.