I wanted to fit inertia real belts, but there were no anchors. The bottom fixing were no problem, but the B post presented a problem because the trafficator was in the way.
What I have done is make a bridging piece from 40 x 6 mm steel with a seat belt bolt welded in from the back and then ground down so that it doesn't foul the trafficator. Then I fitted captive nuts top and bottom and countersunk the steel to accept c/s Allen head bolts to hold it in place.
To finish it off I covered it in vinyl to match the over trims and punched holes so that I can get to the screws to remove it if I ever need to get to the trafficator arms.

I think it’s a good solution to the problem of the anchor being either too high or too low.