You can remove the cooling hose located toward the rear of the head where it connects to the hard metal line on/close to the firewall and run water from a hose through the head and block through the cooling hose, and then run water through the hard metal line on/close to the firewall through the rest of the cooling system. This type of flush can be done with the water pump off or on - if you do it with the pump on, then connect all the coolant hose except the hose that connects to the bottom of the radiator, leave it off at the radiator and connected to the thermostat housing, leave the bottom mounting bolt to the water pump out and some water will run out there, then replace the mounting bolt when through flushing. With the pump off, the water hose flush will pour out the area where the water pump mounts, but will not flush out the entire head area because the head is higher than the place where the water pump mounts. Probably best to flush a bit with the pump off to get most of the old coolant out of the block along with any crud/debris and then after mounting the pump with a more thorough flush since most of the cooling system will be sealed and more areas reached with the garden hose water.
Careful with making the gasket surfaces too smooth. This is 20+ year old technology and designed to have a certain roughness measured in Ra units so the gaskets will hold and seal (more critical on the head to block gasket surface areas). I use a brass brush to polish the contact surfaces and brushing also shows any old gasket material I may have missed!
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The problem with gasket sealer, esp. silicone, is using too much and that is why I suggested using a very small amount . If you are uncomfortable with using silicone then use a bit of grease to soften the gasket a bit and hold it in place (on the injection pump, greasing the gasket is a must since this gasket needs to be pliable and not attached to either surface so the IP can be rotated to set the start of delivery on #1 injector w/o damaging the gasket to prevent the chance of an oil leak), or use another type of gasket sealer (lots of luck with Copper Coat and Permatex Aviation Form A Gasket - but using small amounts), or mount the gasket dry. I've rebuilt well over 1,000 engines (perhaps 2,000) and countless repairs using new gaskets - so I've mounted what 250,000 - 500,000 + gaskets and always used some type of gasket sealer since a leak would cost me $ to repair over again since I was not paid to redo a mistake and, more significantly, the inconvenience to the customer and the cutomer's loss of confidence in my ability to repair their vehicle correctly the first time, or when racing costing a failure and not being able to finish a race, or at the fleet/business level and the loss of income because a machine/vehicle failed and a job could not be bid on/began/completed, or now that I'm out of the professional technician/racing fields my own time to redo a repair. That said, you do what you feel comfortable with.
Texaco, Preston and Zerex make 5 yr./100,000 mile antifreeze. Your M-B was made when the only the green antifreeze existed, so the green stuff will work fine. Zerex is green. Texaco and Permatex are the orange color antifreeze. The orange was made originally for GM applications (GM's Dex-Cool as I recall). Now the orange is formulated not only for GM, but also Japan w/o silicates and Europe w/o phosphates to name a couple of other applications/formulations this antifreeze is made for. Wal Mart just began selling Preston and the label said M-B approved (not on Texaco). However, Preston's M-B application is for the newer models that have plastic cooling parts that are sensitive to certain chemicals in antifreeze that require the orange antifreeze as well as specific pH levels. Also, I use distilled water to make my antifreeze mix (M-B spec 55% antifreeze, 45% water).
The thermostat is another area to consider looking at. Stats get old and fail. If you're so inclined, take the stat out and immerse in hot water at 200 F. It should open fully in about a minute. If bad replace. Check a new stat because they are bad brand new even from M-B (look up a leathermang post about finding all defective new stats at his local M-B dealer), and I've found my fair share of bad new stats also.
Good Luck!
Tom