Oil in the 850 turbo water deposit

Hello good morning everyone in the forum, I hope you can help me? I bought a Volvo S80 850 Turbo Model 1994 in car they sold it with the oil failure in the water tank,
the car starts, according to the previous owner he says that the hit the oil filter and it was emptied on the road and from there is the fault, the head emerged and the joint is fine but I will replace it, that they rectify the head to avoid if the board was twisted, if the joint He was able to mix the water with the oil. or where is the oil filter an cooler? And could it be drilled and is there mixed? or where can it be the most? Thanks for your help.