Valves bent?

How can you tell if valves are perfectly straight? I'm putting an engine in a 3.8 liter Grand Prix,the engine that I got from the junkyard has a cracked head in between where the valves seat. The engine in my wifes car now threw a rod and the valves were hitting the top of the piston,so I'm going to use her heads. If they're bent can I use 2 other valves from the cracked head? I'm going to lap the valves and put new seals on them. The heads I'm going to use had .006 milled off of them,but the block from the junkyard wasn't trued up. If the head was cracked do you think the bottom end bearings and piston rings are okay? It melted the plug electrode and cleaned the top of the piston all shiny,but I don't see any damage and the cylinder walls look ok.

Usually they can be put in a vavle grinder and spot it even before grinding.
They can be checked in a drill or indicated in the guide. If it is still together then fill port or chanber with liquid. If the valves are the same they can be used , but should be ground and have the seats ground too. No idea about the bottom end, sorry.