1990 Mustang GT 5.0 25th Anniversary (Something Wrong With Engine)

I have just finished putting thousands into this car, it was running perfect! Than last week I was driving and it randomly overheated and was shooting out coolant everywhere. I recently installed a new thermostat and it might have closed. Worse case when considering buying this car is that it has possibly has a blown head gasket or a cracked block. It might not be, but consider it does when purchasing. Coolant and Oil have mixed. I can still start it and it will run in idle forever, and I even drove it home after this happened. This is all I know, video included about engine.
I've done a ton of work to this car, interior is amazing. Every Naturally Aspired thing has been done to it. I just bought a new house and my wife is pregnant, i just dont have time for this project now, even though this car was DONE until this happened. I will be taking on a huge hit selling this car, and the person buying it will need to figure out what is wrong with the engine now. I have parts that I will include with the car that i was planning to install such as a 255 fuel pump and shocks. The current fuel pump is fine, but since there is more power and bigger fuel injectors i was going to upgrade that as well.
The list below is what I have done to the car, its this list plus possible some other things I forgot to list, TITLE is clear and clean Maryland Title, I have historic tags which i would suggest getting, cheaper, no emission test and so on
Its a 2 seater now with racing seats and belts. Rear seat delete was done. New mats, new door panels and all, the entire interior was stripped out 3 months ago and redone. There is even the manual in the clove department.
this car has $20,000 worth of work done to it but then again there is a engine issue and here is a video of it running:

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