Small block 340 engine for sale and some questions...

I have always thought the 340 "turned into" the 360. Sort of, it definitely was transformed in the name of emissions. I am curious how well the later 340 performed compared to the early 340. I have had 70s era 318s that were stock except for a cam and header etc that ran really well. Fun on the street anyway. I would have to think the later 340 ran good for what it was. of course in terms of "sale value" the early one is the one to have. Just because it has all the "good " internals. Something as simple as the early high comp pistons vs the later flat tops makes a difference for example. I wonder how many guys back in the day took the later 340 made it into an early or at least switched heads etc.