I have a Quantary teleconverter that I can use on my Canon EOS3 film camera but it will not attach to my 60D body but it attaches to all my other Canon Lenses. I don't want to force it. It seems like the pins won't allow it to seat into the body. Could the difference be that it is a crop sensor body whereas my other cameras are full frame digital!?
The Canon 60D is compatible with both EF and EF-S lenses as it is an APS-C size crop sensor. A standard EF teleconverter will mount on a Canon 60D without a problem. I'm not sure that they are made, but if you were to find an EF-S specific teleconverter that would be an issue if you tried to mount it on a full frame camera such as the EOS 3.
In your situation I don't know of a reason why your teleconverter does not mount.
Note that canon branded teleconverters use the nomenclature extender.