The toxicity of lead has been known for centuries so I would be very surprised if a tin coating was alloyed with lead for something known to have food contact (meat grinders, linings of food cans, etc.).
In terms of stripping the tin from cast iron, this can be done with either mineral acids or alkali but alkali's are more selective towards the tin with the mineral acids attacking both the tin and the iron. There are other components added to commercial alkali based stripping solutions such as chelators which improve the strippers performance. For this reason, I would use a commercial based stripper such as the one made by Metalline Corpooration. I have enclosed a link to their product below: