Window plastic rivet replacement

Hum.
I'll be doing a 67 B body soon. IDK that an A body used the same.
But why should that be surprising?
So, I have no experience and my project is completely apart.
The regulators aren't even in the car.
I would assume it just pushes in. But I would support the back in some fashion.
Perhaps a C clamp would fit around it if it requires that much force.
And then you could squeeze it in.