Each CNC machine whether it be a plasam table, mill, lathe router or what ever has its own unique CAM software "Post". The Post tells the software to export G code for that particular machine. I suspect that G code output for a Plasma Cam is different than what is required to run a Dynatorch properly.
To have any chance of cutting your Plasma Cam G code files you need to convert them back to DXF files and then run them through the Dynatorch DXF file converter or We-cim for the proper Dynatorch G code output.
Do you still have access to the Plasma Cam software and the drawings? You will need it to change the files back to DXF. Make sure you delete any lead ins or lead outs that the Plasma Cam software added when you save the files back to DXF. The drawings must be clean. New leads will be generated in the Dynatorch G code converter. I have a friend with a Plasma Cam and who has given me DXF files for my Dynatorch before which I have run through We-cim. He had to clean them up and save them to DXF before I could cut them.