Do you have a Bayonet style headshell to put on that arm? If the arm is missing the locking wheel that holds the headshell on the arm then you are SOOL!
https://www.lpgear.com/product/LPGPROHEADSHELLB.html
This is what the arm should look like with the locking wheel!
https://www.lpgear.com/product/JELCOSA250.html
https://www.lpgear.com/product/LPGPROHEADSHELLB.html
This is what the arm should look like with the locking wheel!
https://www.lpgear.com/product/JELCOSA250.html