JMHO if you have restored over fifteen Mustang you surely understand shelling out the arguably ridiculous money required for the numbers matching route. Just having the "correctly dated block is near worthless unless you have all the allied components such as: Correct Model Carb, dated intake manifold, dated heads, dated VC's, dated exhaust manifolds, correct model manual/auto dated distributor, dated valve covers, breathers, hoses, PCV tubes, smog pump assembly, etc. I mean really what's the value added for having the correctly dated block and not the correct parts that go with it?..................
Then with a commitment for the numbers matching route typically you are talking show-car and then you are trying to buy/obtain correct original FoMoCo parts for everything from suspension parts, control arms, springs, sway bars, shocks, door panels, shifter, console, dash, Ford rubber body gaskets, Ford Bumpers, etc..........
Finally after you do your ground up correct restoration you go in a judged Mustang show and there's a guy parked near you with a low mileage Mustang that has every correctly dated piece on it right down to the mufflers, tailpipes, wheels etc.... The value of that numbers matching Mustang is typically a fraction of what you spent restoring a car to be worthy of numbers matching..