Yeah you are probably right about rebuilding the old motor.
I don't quite now how much damage the motor has, but my mate said he was sitting on 180 for a while, then when he slowed down the motor started to run rough(would not idle) and after stopping it, it would not start.
It was later found that there was water in the oil, so he decided it must have been the head gasket and proceeded to replace it.
After replacing the head gasket, the f-ing thing still wouldn't start, he took it down to the local mechanic, they did a compression test and found less than 50 PSI on all 6 cylinders(****!).
So i really don't no what is wrong, but the mechanic seemed to think the rings were all melted, i find it hard to believe that all the cylinders could all go at once, is that common?
I was thinking he could of ****ed up the head gasket install or maybe even worse a cracked block.
If i did go the 4.0 swap, i would have to swap the whole motor, manifolds & shit right?