Welcome to the site. Hope you find it useful in your restoration focused endeavors
San Jose Mustangs with VINs like yours were assigned dates of 30J or 01K on their door tags typically.
These dates were assigned as a guess when the cars would be completed when the order was received by the car plant and entered into the computer system. Dates (from examples we've collected) can be off a week or two typically. Sometimes closer some times much later. Furthest off I've got records of is 8 months late
Looking for the latest dated sheet metal panel on the unibody, compared to bolt on panels (this may have been replaced at some point) and engine casting dates and assembly dates will provide a peek into a time period. Figure in the fact that each had to be stamped at the stamping plant (or cast and assembled into sub assemblies ), packaged, wait for a west bound train, the transportation time for the trip to northern Calif, unloaded or the car uncoupled and recoupled to a train going to the Milpitas car assembly plant, inventoried, and moved to the assembly line, then installed.
Sometimes everything feel into place and that process apparently didn't take that long in other examples it took a long time with delays and other issues
Again welcome to the site. There is an article in the Library section of this site on finding and decoding date codes. It is a basic outline but its a start and help for the process
