1: replace the timing cover which will require removing sump,tappit cover injector pump (special puller tool required), timing gears & pulleys, radiator etc. (New timing cover around $650 or used if you can get one thats not corroded $125-$200)
2: Kilkenny casting part number KC41 available at most auto parts suppliers around $70. This part is just glued in to the corroded outlet provided there is enough alloy to glue it to!
I followed the instructions supplied but it failed twice
(due to the fact about a third of the original outlet is missing). On the third attempt I preped all surfaces placed the KC41 in the outlet, I used selleys auto fix knead it to rebuild the missing section of alloy, while the knead it is still pliable take out the KC41 smooth off the inside of the water outlet once the Knead it has set you can fit the KC41 as per instructions, I used three bond super sealer (ps wait until all sealant is dry before filling with coolant and driving, I leant from previous experience
.) Problem now appears to be rectified no leaks!
I hope this will help any other early hilux drivers with the same problem as it seem to be common.