Yes! ABS can be painted with acrylic laquer (standard automotive paint) or Sems vinyl dye (spray) and coat with matte clearcoat finish.

The key to the ease of upholstering is in the stiffness of the fabric itself, the thinner the backing, the more flexible the fabric will be, therefore easier to use.

Designer Door Panels or Trim To Fit Door Panels all would be good choices . We do not pretrim older cars as we don't know several things:

How high the armrest is to the bottom of the window?
In general 9-11" is a good ball park. This way the customer can determine their preference. What I suggest is that they decide how high and where they want the armrest and trim the panel accordingly, regardless of how the panels fit. If I get the armrest where I want it and the panel does not cover the bottom of the Door, I don't worry because I know I will be cutting off the top of the panel and then I can glue it to the bottom of the panel to cover the rest of the Door.