The valve is bent. The piston came into contact with the valve. What causes this?
The top of the piston has slight markings on it. Did the valve travel too far?
Do I need to be worried about the piston?

 

The valve opened too far and the piston kissed it. Very common on an interference engine. Interference means the piston will contact the valve at TDC if the valve is open. The 4.3L is NOT and interference engine. This link explains: Engine Valve Failure

 

So, if the valve opened too far this was caused by a problem with the valve spring being weak, worn guide or something?
I'm going to price having them reworked vs. buying re-manufactured heads. Any issues with getting the correct heads.
I read in hear many times about using Fel-Pro gaskets. Does Fel-Pro make a complete gasket set for heads & intake?

 

 

I was trying to attach images before. So here they are!

 

Caused by something in the head, (guide, valve, spring, keepers, rocker arm, etc). Best to have an automotive machine shop take a look at it and determine the exact cause. Then you can figure out what to do: either have them repair it, or get a reman or used head.

As for the gaskets, need to know what year the vehicle is.

 

Sorry. 2000 Blazer LS 4 door 4WD.

 

If you're only doing one side, you'll need:

1 9354 PT-1 head gasket
1 ES 74034 head bolt set
1 MS98002T Intake gasket set

All are Felpro parts

 

Do you think it would be wise to do both? Doing just 1 would save $$$ but I don't want to end up doing the other 1 in a little while.

 

If the other one takes a crap, you'll end up wasting the intake gasket set and your time to rip it apart again. If you do both now, add 1 head gasket, 1 bolt set, and a head repair. A few more bolts and the other head is off. Not gonna make that call, it's up to you