Trunk Lock 1959 Dodge Coronet
 

Please help! The trunk lock on my '59 Dodge Coronet broke. I believe the guy working on my car, who I can no longer get ahold of, either has the broken lock or threw it away. I bought a replacement "kit" with lock and keys on EBay, but the garage is telling me I need some sore of circular part in which the lock fits into. The mechanic didn't know the name of this mysterious part and of course neither do I.
Anybody know what I am referring to and how I can track down this missing piece. Don't understand why it isn't included with the kit. Thanks.