Newby question for you: Have an opportunity to cheaply purchase an early-80's Mercedes-Benz wagon---a well-kept, dream of a car. The problem: the transmission is broken.

How hard is it to replace the transmission on a 123-chassis car?
Would it be possible for me to replace the transmission on this car myself?
I'm relatively inexperienced in major auto work, but i am not afraid of learning as long as it's not overly complicated. (Previously, i've done all the basic maintenance work on a VW TDI: oil changes, brake changing, sway bar bushing replacement, etc.)

Edit: Found a helpful thread that suggests a transmission replacement takes about 4 hours, and is a relatively easy job. Is this assessment correct?