Both are pretty straight forward.  I have done these on W201 and W126,
both diesel but assume W124 gasoline would be similar.

I would recommend using the drive-on ramps under the front wheels.
Remove the engine mount bolt (hex Allen key, 7 or 8mm, can't remember)
from below.  This is deep inside the cross-member so shine a flashlight
into the hole and find it.  Remove from both sides.

Now come out under the car.  Remove other bolts on the mount from top.
The mount for diesel has two more bolts on top.  I am not sure about
mount for gas engine.  If there is not enough clearance, you may have to
go to the next step first.

Use a wood (e.g. 2x4, or even a thick board) as buffer.  Find a position
to maximize the contact between oil pan and the wood.  Place jack under
the wood.  Raise the engine 1-2".  Do it slowly and keep checking if
clearance is enough, especially at the front fan and the firewall.  The
pan is strong enough to be jacked up this way, though distributing the
weight evenly is very important.  Never jack directly into the pan or it
will crack.

Remove the engine mount.  If there is heat shield, note how it seats.

Installation is reverse.

Transmission mount is similar.  Use the jack/wood to support under the
pan.  Remove the cross member and the mount.  Double check where the
bolts/nuts go before you start.  The two cars I worked have different
trans mount layout.