Matching engine numbers

[915.0]

Ok my mustang is 91 LX 5.0. Sorry its not a gt but I saw your site has info on judging and such. Here's my question. My car is vin 1FACP44E8MF102662. I built another engine for the car because the bearings went out. I want to keep this engine if its the original one. Now the vin number on the block is 1 number off! M102661 is the number on the block. Would that be considered numbers matching or no? My guess is the put the wrong engine in at the factory. What are the chances of this one being swapped in at a later date.

[KS 82 GT]

My assumption would be that it was done on the assembly line. It's possible that the block was swapped in at some point and it happened to be one off, but it would be far more likelier that it was done at the factory. As far as being "numbers matching", the numbers don't match, but if you can document that it was original it would count as the same I would think. It would depend on the buyer. Overall I don't think that is super important on these cars since the 5.0's are common and mostly the same. If we were talking an older Mustang with a 428 SCJ or something, then it would.

On the odds of swapping in a motor one number off, there were two people in my local Mustang club that both built 1966 Shelby clones, both Wimbledon White with blue stripes. They parked next to each other at a show and started comparing their cars and after awhile they realized that the VIN's were consecutive!