Ok, they are stripped, or have no thread, despite the head. Try to access them from the back. If possible. Push the centre pin out with a blade in the slots, at least enough to be able to access them with locking pliers (at the front.)

I am long out of that trade, but in the past I've made all sorts of tools for this sort of job, forked levers, J-shaped pullers, thin wire twist-up loops, etc. Diagonal side-cutters are often useful, used gently, as are electricians wire-strippers.
You only have to move that pin up a little to access it, and the pin often/usually goes right through the expander part.
If you can access a retainer in another place, you can take it apart and study an approach.
They often grip well enough that force will distort the metal they go through!
There are a lot of different types of fastener, and I was never a Ford man. Perhaps JohninKansas can add another approach. This is his sort of thing, too.