i just replaced this engine in my car actually. My old engine crapped out on me with 235k miles with a bad head gasket.That's definitely NOT a good sign! Assuming you didn't add any of the radiator flush/stop-leak type of products, it looks like you have an emulsification of (probably) engine oil and coolant. If your van recently experienced overheating issues, you may have warped your head(s) and toasted the engine. That said, it usually takes on the brown color of engine oil rather than keeping the pink color of the coolant, so the sky may not be falling quite just yet. I would definitely do an oil change to make sure you don't have coolant in the oil. You will need to warm the engine to full temp, do a normal oil change and then pour the oil into a clear/translucent container to see if you get a bunch of water settling on the bottom if you can't tell by it looking like bad mayo. If the oil is clean, I would do a full flush of the coolant and re-fill with Toyota fluid. It's possible, if you take the van someplace like a quick-change oil chain, or some such, that one of the teens working there tried to pour the oil in the coolant instead of the engine, realized his mistake and just didn't tell you.
You know, now that you mention it, my heater and a/c do not work. I wonder if my heater core is clogged. At this point i do remember having heater and A/C issues before the engine swap, way before the car overheated. I did notice the blend doors are moving on the vents inside the cabin but no hot air comes thru.There's still stop leak in the system, remaining after the engine swap. Both heater cores and the long lines running back to the rear heater core hold at least a gallon. Flush the cooling system to get that crap out of there. This guy says buy this relatively expensive flush chemical. I think I'd spend the $20 if I just went through the time and expense putting another engine in my van:
How to Flush Out Stop Leak from your Radiator and Cooling System