For me it still looks like a full rebuild
Need one piston but doing one suggest do all
Heads and everything
Agreed. Engines (and to be honest, any major assembly with many internal parts) get to a point that once there's enough damage, "repair" is no longer the correct term. As much will need to come apart to fix this, at least a minor rebuild is warranted.
(For the next paragraph, I'm going to be referencing the time in 2020 that I did a "minor rebuild" on my 1984 F-150's 300 that had blown 5/6 upper compression rings and chewed the bores real bad).
Not to say that certain things may be checked out and found to be OK, but having a machine shop check out components and do some refurbishing as needed isn't all that expensive. In my case, that was having the block bored 0.030" over (due to the ring/bore issue above), having the head magnafluxed (because boy genius here dropped it in the driveway while cleaning it with the block), having the crank polished (always a good idea when the crank is out), having new cam bearings and freeze plugs installed (because they were removed and nuked as part of being hot tanked), and having new pistons installed on the stock rods (since my wrist pins are shrink-fit). All together (keeping in mind this is a straight 6, not the OP's V8) costing a mere $300. However, since my failure wasn't with the valvetrain, I was able to get away with not messing with the heads other than replacing valve stem seals (since I had all that apart for cleaning).
In this case, obviously there's at least 1 piston needing done and a head that needs serious rework or replacement... that'll require tearing down the short block, so new bearings and a crank polish is highly recommended. And since new piston means new rings, that means checking the bores and seeing if any boring/piston size changes are needed. Not to mention that there may be other valvetrain damage... rockers, lifters, pushrods, and even the cam itself are suspect.
All of this is assuming the valve failure didn't cause any block damage due to metal debris getting scattered. It's very possible the block survived, but nobody sane tears an engine down just to replace a piston... check everything out. But also don't be afraid to not replace non-consumables if they're still in good shape... check everything out!
Edit... low and behold in my YouTube suggestions, here's an example of a head failure (in this case, a dropped valve seat) causing block damage. The shop is able to fix it (that's what they do!), but more damage than initially suspected...
