likelihood of a significant swap-job coming out of 'Triple-E' in Dearborn. I can tell you, for example, about the 1960 Falcon I owned. It belonged, originally, to one of the 'honchos' in the engine section of EEE. When the 289-271 engine was almost ready for production, in early '65, Dom drove it to work and simply wrote himself a pass to take it inside.
When he drove it home a few days later, it had the entire drive-train and suspension for a 271 Mustang in and under it instead of the little 144 stuff. And I mean EVERYTHING!
I had reason to tear into both the engine and the C4 not too long after I bought it, and found it to be stuffed with 'XE' parts, with the numbers scratched into a dab of blue layout dye. I added such things as a 'warmer' cam, and a 'Cobra' intake manifold and 715 Holley I got from Harold Droste.
It was well-used by the time I got it, and had a small leak past the pinion seal in the 9" rear end. I had it up on the hoist in a local 'hang-out' gas station where the owner was VERY impressed by his 440-powered Mopar. He ran his mouth until I offered to run him with the Falcon for the cost of the rear-end service. Although he'd walked all around under it, seeing header collectors and having ordered a seal for a 9", he still had it firmly in mind that it was powered by a little six.