The only time I have seen dropped valve seats in these is when they overheat, either the customer has admitted this or usually you can see discolored metal and sludge through out the engine indicating this is what happened. I have seen a lot butt every time it is overheating.

There is a guy (in seattle I think) that sells bored out 5.7 blocks and calls them 6.1s and I have heard of others doing it and using STD 6.1 pistons.