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I got this info from the other Tbird forum I belong too.
Numbers matching" typically meant that the engine was stamped with a portion of the car's VIN in order to tie the car to the driveline. In Ford's case, this wasn't done during the '50s and '60s until the '68 model year, but that's beyond the point of this response. The closed you can come to "numbers matching" for a Ford product is comparing assembly and component dates. Components of a car can be evaluated against its final assembly date to narrow down whether or not they may have been orignially installed it.
Date codes in castings, date codes in glass and sheet metal, assembly date codes stamped into engines, assembly date codes stamped into ID tags for transmissions and rear axles typically should not be more than a few weeks older than the assembly date on the data plate, and certainly shouldn't be after the final assembly date. If a date code on a component part is significantly outside of the window of car's production timeframe, chances are it's a replacement part from another car. But like with anything else there are exceptions, such as a large run of glass manufactured and stockpiled several months before being needed at final assembly.
For major components which have an assembly date stamped into them, like engines, transmissions and rear axles, the closer the date is to the build date of the car the more confidence a person should have that it's original, but the exact time frame of when the component was assembled versus the car's assembly date would need to be studied. In short, though, it would not be a positive match. Only knowing the car's history from the date it left the assembly plant to the present time could give a relatively certain degree of confidence that the engine or whatever is original to the car.
Bob.
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