Refitting lap belts on my 1993 Hiace H100 camper

After some help/advice/guidance if possible please:

I have just purchased a 1993 Hiace GL Yokohama conversion. It has 2 bench seat in the back which seated 5 people or transforms in to the bed.

Once upon a time it had lap belts fitted for the rear passenges, but at some point during it's (long) life they have been removed. The anchors in the floor still appear to be in place.

I would like to reinstall lapbelts so any rear passengers are safe (as safe as lap belts can be) but I am unsure where to start. Has anyone done this before or has experience?

My neighbour is a pretty handy mechanic who will assist, but he said he needs to know the length the seatbelt webbing etc. needs to be.

Could anyone supply me with any of the dimensions or pictures if they have a similar configuration?

Thanks in advance

Definitely a mistake to use the word safe with lap belts. Fitting retractable shoulder belts and treating it as a 6 seater would be the only advice I could conscienably give. For securing an infant seat they’re fine but not kids or adults.
My SC has a lap belt in the center seat of the middle row but it’s fixed to the seat itself, not the floor.