....... I am leaning towards five point harnesses.........
Contrary to what might be said, the 5th point is what makes the harness most effective. If you do not have a crotch strap the lap belts will pivot upward when you are hanging upside-down or thrown upward in a jolt. This lets your fanny come off of the seat, so the tendency is to cinch up harder on the shoulder belts. This will keep you from being able to move your torso to look alongside or back.... very uncomfortable....
The crotch strap keeps the lapbelts down and anchors you to the seat by your pelvis, allowing the shoulder straps to be a bit loose for mobility. The shoulder straps are only there to keep your torso from being flung forward or out the side. The crotch strap is a real plus in my opinion, and yes, I have hung upside-down in the harness.
Here are some pix, as to one way of anchoring that 5th strap. It seems that the newer Crow harnesses come with a much stubbier anchor plate than they used to. If you find that yours are shorter than the one shown, you should be able to get longer ones at an auto parts store (at least one that handles safety gear).
The lacing should be done with the 'loop' away from the seat latch handle, else the seat might go click
Use a low profile bolt, but even so, you will need to do a little filing on the plastic latch frame.