It's quite hard if you don't know Calculix keyword and its structure.
In your input there is an *assembly, Calculix has no such a keyword and like this many other differences. It's tricky to think that Calcuix is the same of Abaqus. It's abaqus like but it's not.
I tried your advise as described above, i.e., mark the checkbox "Do not use parts and assemblies in input files" prior to exporting abaqus inp. However, after importing the inp file in CalculiX CAE, it failed to produce .frd file after I click on the submit button.
May I know how do you carry out exporting inp file from Abaqus? I did it by right clicking on the Jobs > Manager > Write Input. Is this method correct?