Disclaimer: Pardon my ramble below
How is this cert recognized as being for a modern build? Because it has a CSM number on the cert instead of an SFM number? I'm trying to learn for future reference.
CSM would potentially be a "licensed" build from modern day SAL (Shelby American Licensing) where a 3rd party company or bodyshop (just about anyone, not Shelby American Inc themselves) paid Shelby licensing to build a
modern day replica out of an old Mustang bodyshell. Anyone with a deep enough wallet can do the same, with or without a CSM certificate (basically wall art these days)
https://www.shelby.com/carrollshelbylicensing/In this case, you have enough experience with Ford products to know it was an original 6 cylinder "T" code chassis.
Again, just based on what you have posted above, it appears that a CSM number was used on a certificate, but apparently the car has not yet been built, or was built, then sold to someone, who now believes they have some "special hidden gold" in a 6 cylinder chassis. I believe, with your experience with restorations, that you already knew the answer before you started this thread, but doing your due diligence, found this to be exactly what you thought in the first place.
Bill