[71GMC_3/4T]

I did mine when I was putting the new headers on.
I used a block of wood under the oil pan. I had it almost up enough when I realized the fan was really distorting the fan shroud - aaack! Pulled the top half of the shroud which allowed it to come up a little further.
The bolts up into the block were a real bear since the rubber of the mount had squished into the sides of the holes after 30 years. I was able to use a pry bar to force the socket up enough to get the bolts out though. You will only have 2" to work between the mount and the bracket. Be CAREFUL! Don't put your fingers in between the surfaces unless you don't have any use for them any more. Also, be sure you have a jack you can trust and not some tywanese cheapie.
I found it easiest to leave one mount loosely installed while I did the other mount. That way it rocks up the side you are working on farther. Also makes it easier to line up again when you let the engine down.
Only took me one six pack to get the job done... But then again, I got the right mounts from the store!
Good Luck!