What car/engine?
The HG is only severely prone on the M5x engines, by comparison M30/60's are quite rare. The M30 is dead simple to HG change, you just need two sturdy blokes or an engine crane to do it in a days DIY. The M50 is less simple, but still doable in a weekend the first time around, but requires some specific tools.
Additional items needed for either: Broom handle, roll of string/twine, (M50)torqx sockets, (M50)very narrow body torqx sockets for the front of the head and tiewraps to fix the chain to the top sprocket.
If it has blown and you keep driving it, it -will- crack the head, no questions asked, in a matter of hours.
They -could- easily be unrelated - during winter time the E34 is prone to billowing steam out of the exhaust anyway because it's got an absoloute monster of a double skinned exhaust system on it which can take more than an hour to come up to full temperature. There's millions of places coolant can go missing too...