Mississippi is one of many states that allow a state-assigned VIN. Take the vehicle to your motor vehicle agent for a VIN inspection. If they cannot locate a VIN, they will assign you a new VIN number and attach the corresponding tag to your truck. You need only supply an affidavit explaining why the VIN is missing. In your case the truck's age alone should constitute sufficient cause.
Here is a link to the MS State Assigned Vehicle Identification Number form:
https://www.google.com/url?sa=t&rct=...0EHEA-j9diBWPC
Here are the instructions; Section B1 (missing) would apply to you:
APPLICATION FOR ASSIGNED MISSISSIPPI VEHICLE IDENTIFICATION NUMBER
ALTERED, REMOVED, OBLITERATED, DEFACED, MISSING, OMITTED, STOLEN
Sections A, B, C and E must be completed if application for a Mississippi Assigned Vehicle Identification Number is for reason that the original plate is altered, removed, obliterated, defaced, missing, omitted or stolen.
A. If reason is defaced, altered, obliterated or removed, the following supporting documents must be submitted:
1. The vehicle identification number plate.
2. Affidavit by owner stating the circumstances by which the vehicle identification number was defaced, altered, obliterated or removed.
B. If reason is missing, omitted or stolen, the following supporting document must be submitted:
1. An affidavit by owner stating the circumstances by which the vehicle identification number plate was missing, omitted, or stolen. If and when the original plate is recovered, it shall be surrendered to this department.
Upon approval of application, a Mississippi Assigned Vehicle Identification Number Plate will be issued. A representative from this department will inspect the vehicle, deliver and attach the assigned Mississippi plate. After the Mississippi plate has been attached to the vehicle, owner must take form 78-602 to a designated agent (local county tax collector, dealer, or bank) and make application for a certificate of title.