Well, the thermostat change went nicely!!
Many thanks to the folks on this forum Koningster, and mtrevelino for your comments and your references..
Koningster referred me to a GOOD writeup here: HOW TO: Change thermostat - OM648 (W/S211 320CDI) - MBClub UK Forums
Many of the instructions were followed from the writeup, and here are a few of my observations and changes:
1) In the writeup the guy placed a rubber glove over the oil filter hole. I tried that but didn't like the fit so I looked around and found a cup from a happy meal.. The small size empty drink covered the hole perfectly and I folded the excess inward..
2) Like others have said I replaced the antifreeze lost in the change with 1/2 gallon MB anti-freeze, and 1/2 gallon water.. It was easy refilling the unit with everything together. I filled the reservoir and squeezed the upper radiator hose. This seemed to force the air bubbles out of the system and I was able to fill to the top of the reservoir's internal baffling..
The unit has the 3 bolts but the other two that hold the part in place were not pre-tapped holes for me either. No worries as the bolts went with no problems..
It took me around one hour from start to finish..
Now, the car heats up to the proper operating temperature and the mpg on the computer is higher.. Much higher. This definitely works for the better!!
Thanks again for the help everyone!!