I guess I'd better chime in! That unit is the one you're looking for if you want to drop the rear ratio to a more bearable level. I'd recommend getting it as complete as possible (preferably with traililng arms, etc.) just in case you mangle some bolts getting the old one out. I started my swap back in February, but have been taking my time as I wanted to swap out as many bushings, seals, etc., as I could while the thing was out. Occasionally,. certain bits would take a while to come in.
You'll need to get the speedo recalibrated if you want it to be usable. That'll run you about $150.
How many miles are on your 250?
John
John Livingston
Newport News, VA
1968 280SL 4 speed manual