Volvo Repair: 264 VOLVO 1978, combustion chamber, head gasket

Question
THIS CAR ONLY HAS 75K MILES THE ENGINE HAS DEVELOPED A WATER LEAK . SEEMS TO BE LEAKING INTO THE COMBUSTION CHAMBER.THE CAR RUNS ROUGH AT LOW RPMS BUT RUNS FINE AT HWY SPEEDS. I HAVE PUT SOME TIME INTO THE BODY ,BUT HAVE HEARD NOTHING BUT BAD THINGS ABOUT THIS ENGINE.I NEED SOME REALISTIC SUJESTIONS.PLEASE HELP , WINTER IS COMMING FAST, CAN'T KEEP POURING THE WATER THROUGH THE COOLING SYSTEM.  

Answer
These motors had bad reputation before, because of customer neglect. The oil passages to the cylinder heads were designed too small and were prone to clogging if customers did not change oil often enough, which led to the camshafts premature wear. Also they required a little more maintenance than four cylinders. Other than that, they were known to last a few hundred thousand miles.
Need to confirm that water is indeed leaking into combustion chamber by pressure-testing cooling system. If so, might be from head gasket. This will be an involved job that needs know-how and special tools (to lock the chain and liners in place.)

One option if this is the case, have known people to remove engine and install a used or rebuilt four cylinder in its place. Must transfer the computers and harnesses over to convert the six into a four.