I agree with you 6T09KGT. BTW, I have owned 6T09K201478 genuine K-code fastback GT (as determined from its body buck tag that has PIO on it) for nearly 25 years.
Since my first post, I have pulled the front fenders off my 65 coupe purchased last month, and have pulled the engine and transmission. I'm now 99.9% sure that I have a counterfitted K-code, where the 3 VIN's on the top of the aprons have been welded in, and the matching door tag is on the door. One of my sons has a restoration shop, and when he looked at the aprons, he imediately noted that the metal around the VIN's had quite a few rust pockmarks, while the remainder of the aprons have none. The body of the car, including underneath, appears to be quite rust free and very solid. I know what Mustangs that have lived in the Rust Belt look like underneath. I have a 68 J-code covertible that I did a huge amount of under-body rust repair on. Per the K-code VIN, the K-code car was sold to the Pittsburgh DSO and the car's history back to at least 2015 is from Pennsylvania.
The former owner sold it last Fall at the Carlisle acution, it was bought by a classic car dealer in western PA, who had it listed on his website for a while, but sold it at Mecum in Kissimmee where I bought it over the internet. The classic dealer didn't do anything to it, because it looked just like it did when it sold at Carlisle, including the K-CODE decal on the center-top of the windshield. The previous peronal owner's title shows that he had owned it from Sep 2015 until Oct 2024. I googled his name and he appears to be a software developer for the state of PA, so I'm highly suspicious that he never knew that he had a counterfiet. At this point, it doeosn't make any difference, and I probably won't burst his bubble by contacting him. I'll probably never sell the car, and if I do, I'll be honest about what it is.
I'm certainly disappointed to not have a real K-code body, but my purpose for buying it is to have a car that runs like the 66 hipo coupe that I had back from 68-70, since my 66 fastback is fairly heavily modified in drivetrain and suspension for track use.
The 6-bolt 289 had obviously been rebuilt, as the head bolts were ARP's. The head's are not hipo, but the rebuilder had installed screw-in rocker arm studs. Without removing the heads, I changed the valve springs to hipo spec springs, put retaining cups udner the bottom of them, checked the load of each spring at spec heights and shimmed each spring to hipo spec installed loads.
The piston bores have been bored .030". Looking down through the spark plug holes with a bore scope, the cylinder walls look good. It has pop-up pistons, thus it's better-than-expected compression readings before I pulled the engine. The standard rods already had ARP bolts, which are stronger than the stock ones, so I could torque them to 35 Ft-lbs, instead of the stock 24 Ft-Lbs.. I installed ARP main studs, which will be stronger and have more pre-load force than the standard main bolts, to hold the standard main caps in place.
Of course, I installed new rod and main bearings and torqued the ARP bolts and studs to their specs with their special lube. I installed a Howards repro hipo solid lefter cam, to replace the similar-lift hydraulic cam that was in it. I also bought a NOS hipo timing set with the narrow chain and hatchet counterwight off of eBay, and re-installed the hipo damper that came on the engine. I hope the balance is good enough to comfortably rev it to hipo rated RPM of 6000.
I also installed a repro Cobra intake and 600 CFM Holley double-pumper, like I had on my 66 coupe "back in the day".
The transmission is a wide-ratio Warner T-10. Since I have a close-ratio toploader (with the VIN 5F09K602281 stamped on the bottom) that came out of my 68 J-code convertible, because the transmission growled due to bad bearings, I'm rebuilding it to put in the 65 coupe.
I don't think the rear axle is from a Mustang, because it doesn't neck down in diameter where the leaf springs mount. It is a 9-inch with 3.89 gears and feels like it has a locker differential in it (can spin one tire forward with the other side locked, hearing a ratching sound, but if hold the driveshaft, both wheels lock up if try to turn them backwards. I'll deal with the rear axle later after I get the car runnning. I'll at least change it to a stock 3.50 hipo ratio. I'm hoping that the stock driveshaft out of my 66 fastback, which got an aluminum driveshaft years ago, fits the 65 coupe.
More later after I get the car running with the rebuilt engine and transmission.