I Have a problem with the power steering, 1967 Firebird.
When turning the wheels fully to the left and then starting the engine, the wheels
turns automatically to the full right position. It is impossible to turn the steering wheel back to the left as long as the engine is running but possible with the engine turned off. The pump has not been running since early nineties, just filled
up with oil and made sure all air was ventilated.
Any ideas ?

Sounds like it's not the pump. Must be the valving in the box itself might be stuck. Only thing you can do is work it back and forth for some time and let the oil soak in till it frees up. If that doesn't happen you're looking at a rebuild or a box replacement.

Thanks.
Will try that.

If that doesn't work, maybe replace the powersteering oil, with synthetic oil.. -It should be better than 'normal'.. worth giving it a try..