Sun Valley MB at 1-818-768-0704, svmbz@alo.com has complete rebuilt and tested 450 transmissions and torque converters for $1050 plus about $50 shipping. I think the price for a 300d trans. wouldn't be much different.

I got a rebuilt trans. for my 115/300d from another company (I can't remember their name) for $1050 but the converter was $200 extra. All the tramsmission co.s I checked into locally wanted 'big bucks' for a MB trans. althought they said that they would install an owner supplied one for $275 to $325.

It took me about 4 hrs. on a gravel driveway with a 50 year old floor jack and a couple of sheets of plywood for a floor to change mine out. You have to remove the driveshaft which takes a bit of time. Leo is right about the 24" extension to get the top bolts. You also need the same rig to install the top bolt in the starter. I think the Allen socket is 10mm.

Before you start remember that there is a drain bolt in the bottom of the converter which helps cut down the mess a bit. The converter has to be slid back on the trans. output shaft before you stab the trans. in place. Once the trans is in and bolts in place then slide the converter forward to bolt it up to the flywheel. You access these bolts through a small hole in the front of the bell housing.

Good luck.