There are a couple of guys in the US with M60B40's that have clocked over the 400k mile mark. Overall so long as it is a B40 the M60 is a really strong and reliable motor. (The B30 on the other hand it a piece of rubbish)
Cylinder bore issues never effected the cars in SA.
Make sure the first thing you check should you get an M60 is the oil pump, both the bolts that hold the pump together and the bolts that hold the pump to the block rattle loose.
The gearbox is one of the strongest that BMW has ever used and unless you drive like a complete chop will outlast everything else on the car, except the diff.
Clutch you will probably look to replace every 100-150k km, the DMF could probably last two clutches as it seems to have been made stronger that the ones on the younger models. New clutch and flywheel will set you back around R15-20k.
Depending on condition you will probably have to spend around R30 - R100k to get it into a decent condition. Also keep in mind that it is a V8 so there is more of everything to replace. The filter cost about double of the I6 equivalent.
Also keep in mind that most things even filters have to be ordered as they are no longer actively stocked by the dealers (except for existing stock of course)