I just did the head gaskets on my D2 and although I didn't find any gooey sludge as shown in the pictures. I did find that my expansion tank cap was deteriorating and breaking apart and the forward end of the driver's side head gasket (where it was leaking) was clearly eaten away and corroded by something.

I flushed and refilled with standard green anti-freeze which I've used in my Alfa Romeo (that also has an aluminum engine) for the past 35 years without problems. It is a bit harder to see the level in the expansion tank but overall I feel a bit better about it.

This has been a good truck but has always been plagued with small, ****ling coolant leaks. With all new hoses, head, intake and throttle body gaskets I'm leak free for now. Time will tell if the absence of Dex-Cool will make a difference. The cooling system does seem to be a bit over complex and troublesome but when it works it performs as advertised. It actually took quite a bit of adjusting and fiddling to get the new hoses to stop dribbling around the thermostat. I had assumed the spring clamps would be superior but gave up in two spots, installing high quality marine style worm clamps instead. I don't generally like to use screw clamps on plastic (thermostat) but in this case I seemed to have no choice.