Front centre seat belts

Not too happy with the lap belt for my son when he is in the front centre seat.
I have a new 5 point harness which was made obsolete for oval racing.2" webbing like normal seatbelt and a quick release aircraft buckle. In red.
Anyone fitted a five point? the front crotch/lap strap looks to be the biggest hassle, though a suitably large spreader plate and the correct grade bolts should keep it MOTable (Kitcars can use racing harnesses as I understand it)
Any thoughts would be welcome,
Cheers,
Jim.

You also need to fit a sturdy anchor point for the upper straps that's above the height of the seat. Don't just loop them over the seat with no upper anchor- the forces in a crash will all be in the wrong direction, pushing the occupant downwards.
This image from Exmoor trim is a good example of how not to do it: