The way that caster is changed on the 240s is by using ball joints with a different offset in the ball joint from the mounting holes. The early non-powersteering 240s used a ball joint that was symmetrical - i.e., interchangeable left or right. The power steering models had additional caster added to provide more return to center force through the use of offset ball joints. Of course, if you have the wrong ball joints on the car, you would end up with caster of about 2.5 degrees. Installing the correct ball joints on the wrong sides results in a caster of about 0 degrees. If you have the car lowered, it should increase the caster angle (same offset, shorter strut length). The smaller caster angle should make the steering feel a bit lighter and give more of a tendency to oversteer. The only way to change the caster angle would be to slightly slot the lower control arm where the outer two ball joint bolts are so that it can pivot on the inner bolt. Moving the ball joint to the rear will increase the caster. A little trig along with the rest measurement of strut length from the upper pivot will tell you how much movement is needed.

Other things that can affect caster are damaged front components like cross member or front frame. Was your caster the same on both sides?