Manual steer tight near locks

how much positive castor do you have. if you set it up as per the factory book probably none or very little.
if you used the modern thinking and added some to get a more modern feeling, self centering action to the steering, or indeed the most you could, without positive camber. Then anywhere away from centre, the action of steering is LIFTING the front of the car, and this LIFT increases as you get closer to each lock. That creates a bigger effort necessary to steer. Check also, espcecially if you have increased wheel or tyre width (and diameter), that you are running the correct pressure. i run a relativly skinny 205 65 front tyre and a 16:1 manual steering box, the difference in parking speed steering from 26 PSI to 34 PSI is dramatic. you really need to know the weight of the car the designed pressure for the, now radial, and not cross ply tyres, and get a proper value. it will not be the value that the book states for your car with the orginal OEM tyres, it may be close but it won't be the same, in my case i end up at 34, tyre can take it for weight and speed rateing, car is light, yours may not be , a few psi higher aint gonna be an issue but might make all the differnce. but check weight and tyre rateing before going mad with the compressor.

if you jack it up and steer it to check, make sure upper bump stops work for the upper arms. if they are crushed and too soft, missing or the ends are snapped off, the suspension droop will be too much and you will over articulate the ball joints, the whole lot will bind as the studs hit the sides of the holes in the joints, it will feel horrible but is not really testing what you want to test, just illustrating you have a bump stop issue.

Dave