Larry, I hate to be the bearer of bad news but I fear for your bearings. I have a 944 Turbo, these have a seal problem that if not updated will allow coolant to mix with oil in the oil cooler. If you find an oil/water mix in this car you replace the seals AND bearings. The water can very very harmful if the car is run. The loud thunk may very well have been a rod bearing siezing. Hopefully the bearing didn't spin, then you could concievably just replace bearings. I do not think water in the cylinder is what caused the noise. Often when the gasket goes nothing gets into the cylinders but it does allow oil to mix with water. While overseas maybe it would be best to find a low mile used motor an ship it back. The exchange is so good you may save money over a repair especially if you need to do the bottom end. Best of luck and get that 5 speed back on the road soon.
90 300GE 5sp
86 944 Turbo