A lot is going to depend on the condition of the cutting edges. They may like Andrews be new taps that have just been stored poorly in which case cut off the bend, grind a square/flat end on them and you are good to go.
However if they were taps that had served their useful production life then they may not be much use, the costs of snapping a blunt tap in an expensive casting may make the bootsale bargain not so good after all.
Best thing to do is try and establish what the threads are then once you know the correct tapping drill size try them in a bit of scrap material to see what they cut like though a close inspection under a magnifying glass will give a good indication if they are blunt or not.
J