[prairieschooner]

The 6V92 is designed to be able to have an in frame rebuild but this would only be typically. With the looks of the pieces it may be wise to look at the crankshaft and connecting rod bearings. If the pieces have been able to circulate them it could have done damages that would be consistent with a complete rebuild. Having stated this then I should also suggest that you use the recommendations of your mechanic because he/they will need to stand behind their work unless you request something different giving them a way out.
I am not so sure that 1000 miles could have done this much damage although they should have seen these pieces if they were present during the previous oil change.

I do my own Oil Changes. I just go to Walmart and buy a plastic container (one of those inexpensive storage containers) that is low enough to fit under the engine and hold the 7-8 Gallons (sorry but I cannot remember exactly but I think I remember about 6-7 Gallons). I then put down a plastic tarp and then the newly acquired plastic container. After the container is in place I poke a hole in the Filter (be sure that it is the Engine Filter and not the Transmission Filter) to allow it to drain before I remove it. I then use a Plastic Bag and remove the Filter (the Bag only helps keep the area clean). Now I replace the Oil Filter, and drain the Engine Oil, I usually let it drain for quite a while because I do not feel the need to warm up the engine. Replace the Drain Plug and Replace the Oil.
I then clean the plastic container and dispose of it along with the spent filter. I have a 5 Gallon Plastic Fuel Can that I put the spent oil into and take it off to a disposal site usually O'Reillys because they are close.
I buy 10 Gallons of Oil when doing this because I change the Generator Oil at the same time. This way I have a couple of gallons left over for the road.

Good Luck! remember hindsight is always 20/20 and advice is only worth what you pay for it.