what would be the best and easiest motor and transmision combination to put into my 1970 datsun pickup truck

 

I would have to imagine that the easiest combo would be to replace it with what came out of it...

But if your looking for something fun stuff a small block chevy 350 and a th700r4 in there. Yes its possible... we have that same combo sitting in a 240Z we lovingly call "moneymaker" for obvious reasons.