340 with metal in oil pan

12swinger said
The spare parts could have been in there all along.
The valves crashing had to be a miss or some obvious lacking?
If the bearings looked good, may be able to flip the piston, if the rod is even on right.
Get the heads looked at.
Got luck could have been worse.

Broken valve retainer parts and pistons with valve strikes go together. The engine has a “knock”, the pistons upside down. This is not a coincidence.

Krooser said
Fix what's broke if you don't want to spend $4,000. Nothing wrong with that. You don't NEED aluminum heads, Chinese rods, etc tonnage a good running engine. Just my humble opinion.

No, you don’t “need” those parts. But if you start pricing out what it will cost to have the old stuff reconditioned and machined you’ll find the new, much improved parts aren’t out of the ballpark. In some cases, like the rods, new is cheaper. Reconditioned rods with ARP bolts cost as much as new stuff, which is lighter too, reducing the rotating mass.