I have the exact same car (79 240D) and did the two motor mounts a couple months ago. Still have the T-mount sitting in my garage waiting to get put in.

Remove bolts, jack engine up with a piece of 2x4 under oil pan, slide old mounts out. Engine should be jacked up enough you should be able to slide the driver side mount in (less access). Then I found the trick to getting the passenger side in is to grab the top of the valve cover literally push the the top of the engine toward the drivers side to gain clearance to slide the passenger side in... (I was using a large pry bar with one hand and trying to slide the mount with one hand to no avail...)

Remember removing the air cleaner assembly is a must with the passenger side. Please let us know how it goes, especially the t-mount as I don't even know how to install, just noticed the mount was shot when I was replacing the oil pan gasket...