I know this isn't the best place to seek answers, just hoping someone might be able to help out.

On my 1975 TD Cortina the steering shakes really bad whenever I get the car up over 90ks.
I've looked over it all myself and gave it to my mechanic to look over too.
He found that the upper control arm bushes were a bit buggered so I had them replaced.

Problem is, they must have been a side effect of the actual problem because this only reduced it, I fear the new bushes will be buggered soon and it will be just as bad again.

I've changed between 3 sets of wheels, the steering rack isn't great but it's far from gone.
ball joints seem ok, they don't rattle or crunch.
All other bushes are tight.

Any other ideas? is there a change the hubs could be slightly bent or something?

Cheers.

Silly question, but the wheels have been balanced correctly yes?

Yep, I should have mentioned that.
I've tried a few different sets of wheels aswell.

13" steel rims.
15" alloy rims
and it now currently has 15" steel interceptors on it.

They all do it.

Not 100% sure on front end geometry, but could be front caster arm bushes / the radius rod bushes. I know commodores have the same problem when their bushes go kaput.

Cheers mate, I was hoping to avoid rebuilding the front end, I really don't want to do it all only to find out it still does it.
All that work and money for nothing.

what about wheel alignment? when did it have one last?