Bringing this thread back from the dead since I finally have the car running again after a full re-shell. Since all the hardware has been transferred to the new car the issue is still there but it is actually worse now. At some point (maybe only when the engine (or steering oil) is cold there is a judder through the steering when turning the steering wheel. And besides that it is still very heavy without much feel in the steering, perhaps even more than it was several years ago.

So I've been reading up on how power steering works and it is actually not that difficult. This video gives a very good explanation:
But it makes me wonder why the amount of assistance would be different between the different versions of the Sierra (Cosworth). As far as I know all steering racks have the same internal dimensions for the piston, so with the same pressure from the pump they should have the same amount of assistance. I guess there must be something wrong with either my steering rack or the pump. It's just a shame I have to use a 2wd Cosworth rack because I have too much lock with a regular Sierra rack. It seems the lock stop on the passenger side might be exchangeable since you can removed it to remove the actual rack from the housing. But I think on the driver side the lock stop is just part of the housing.