can the rear shocks on a w123 be changed with the rear wheels on ramps?
 

or do i need to have the rear jacked up with the wheels free in the air?

Yes. The only tricky thing is to be careful with the lower bolts. They sometimes rust solid and break off so use penetrating oil and take your time getting them out.

Torque on lower shock hex bolts is. 45Nm or 33 ft. lbs. Top, to thread runout.

"can the rear shocks on a w123 be changed with the rear wheels on ramps?"

Yes

"or do i need to have the rear jacked up with the wheels free in the air?"

No

Here is a pic of one of my Rear Lower Control Arm Bolt that sheared off.

Even drilling and an easie out would not remove it. I ended up drilling it to an SAE size for a new Bolt.

Note the above is not something to do with it on ramps or even with the Wheel still on. Need lots of room.

Used never siez on the threads so it would not rust up again.

thanks very much for the replies and the torque values!