The anti sway bar has absolutely no effect on steering effort so don't bother fiddling with that. Wheel offset will affect steering effort as will tire sizes - the original tire width was 165 mm. If you have fitted wider tires finding some good quality 165 tires will help. I think Vredstein makes some period correct tires in 165; but, they are not cheap.

The 140 (and all other similar vintage Volvos) come with the absolute minimum amount of positive caster that is safe. I think the factory spec is 0 to +1 deg caster. Increasing the positive caster increases the self centering / stability of the steering at higher speeds; but, increases the steering effort. If you do a suspension alignment check make sure that your caster is within factory spec. Adjusting to the least amount of caster (0 deg) will reduce the steering effort; but, may make the car a bit of a squirrel chaser at highway speeds.

Check the steering box adjustment. People have tightened up the pitman arm shaft adjustment of the steering box to remove steering play and if they over do it this increases steering effort. The service manual describes the correct adjustment of the pitman arm shaft adjusting screw.