I use solidworks and download the PTC version. Open the part from solidworks. (if it doesn't show up in the folder you downloaded it too, change the bottom right drop down menu to "all files") It will take a few minutes to open and show the field. but then just "Save" and it converts it to a Solid works part. the field file name is "field_assembly_top_level". Worked for me, hopefully works for you
. To prevent everything from moving Mate it as a Lock, by highlighting the whole field, and mate as "Lock". if you want the bridges to move it will take a little longer to do that.