I have a feeling that all that your car needed was a pair of rebuilt heads and the new timing chain and tensioners.The bottom end on these cars are good for 500-750 k if taken care of.The block is made of an aluminum/silicon mixture thats causes hardly any wear in the cylinders.In other words ,the "bottom ends" of these engines were built to last.
but dropping in a rebuilt 380 is not a bad way to go.
then nothing to worry about.
Sticking with the 380 engine is a wise choice.
Good job for saving an old 380 SE !