Killed my 240D yesterday :(

[uneasysunday]

Was driving yesterday, getting on the freeway for a little 5 minute jog to work. Realized I didn't have any heat coming out the vents,(should have pulled over or taken next exit). Watched as the temp gauge slowly started to rise but not overheating at that point, not even at 195-my thermostat temp. Got off the freeway after a couple of minutes and the temp gauge continued to rise...

Sitting at a red light right outside my work the gauge popped to the red (as if it had been giving me a false reading for a minute or two). pulled into the parking lot at work, shut the car off and popped the hood to find my car steaming and coolant all over the engine bay.

By this point I needed to start work, so I gave a quick inspection but found the hoses were good, radiator cap seemed good but the cap is where I suspect all the coolant came from judgeing by the splatter on the inside of the hood.

Went out to my car about 4 hours later on my break fearing the worst. Went to crank the engine and it wouldn't turn, My heart sank.... Lucy (my 240D) is my daily driver, a true road warrior with 300,000 on the body and about 100,000 on a engine that ran perfect.

I took a few minutes to collect myself and realize she might be done, went out to try to crank her again and she turned. And then, started to run- sounded like she was only running on two or three cylinders at first and then all four after a few seconds. I have never heard this car run so ****ty, even on cold starts in the single digits. White smoke was billowing out of the tailpipe(a sign of coolant in the combustion chamber)

Today I inspected the dipstick and it appears the oil is clean, its got good oil pressure so I think I haver hope for this engine. I am thinking for sure it is a head gasket letting coolant into the combustion chamber but am unsure of what caused the overheat in the first place? Could the head gasket be the original culprit, using all the coolant before I noticed? I am pretty sure it is not the thermostat due to the fact I did not have any heat coming out of the vents and the line to the heater is before the thermostat?

Benz gurus please chime in, I have multiple vehicles to drive but I wanna fix this old girl and get here back as my DD

After I verify the head gasket leak with a combustion gas tester I am thinking I need to put in:

Head gasket, timing chain, water pump, timing chain tensioner and guides

Please help! I have been looking for a good writeup online for a headgasket fix on a om616 or 617 but havn't found much, its always good to get your bearings on a project like this before you actually start turnint wrenches.