The "head" of the key is not important (other than for possible cosmetic issues and model year use. What IS important is that stamped letter below the head, on the shank.
That letter identified the groove pattern on the key. The grooves vary with different ID keys, as to specific placement of the groove on the shank, even its width. ALL of which must match the innards of the key cylinder exactly to go into the cylinder and then turn.
IF the turning part is a bit off, it can result in keys that take some finagling to get to turn. This can be due to one or more of the cuts on the key shank not being exactly what the internal tumblers "want to see". When all is correct, the spring-loaded tumblers "fall into place" to allow them to not hit the innards of the key cylinder and then turn easily.
As mentioned, the wire brush can be used to smooth things out on the key so things work better.
In key blanks, there were only a few companies that made them, back then, to Chrysler specs. There were OEM and "replacement", but the main differences were cosmetic, if you knew what to look for. Still, the letter codes on the shanks need to match, IF there are any. There are online and swap meet vendors that sell the OEM-style keys.
Rather than trust the "Use Charts" on eBay, you might use Google to look for images of the keys that actually fit the different cars. Possibly some archived posts in this forum, too.
Enjoy!
CBODY67