The issue with the car on Texas Car Wars was that there were signs that the chassis number on the inner fender had been welded in after the fact so they called in the trooper who found other places where the original id was. A V8 id had been put on a car that was a straight six car according to the number found in another part of the body. The Trooper concluded that the car was probably a stolen car and impounded it. No word on any outcome.
People have tried to import modern versions of a older car like the 2cv and original Mini which were made in other markets much later than for the U.S. but California in particular is on to the tricks and the ways to spot a late model one are known now. You might be able to get a title from a state like Florida or Arizona but it doesn’t make it U.S. legal. Swapping in the I.D. of an older model only works if nobody knows what the newer models look like.
A few years ago you could buy a kit to rebody a 80’s or very early 90’s S-10 Blazer 2door where you kept the cowl,windshield,and front doors. But then you put a kinda sorta 30’s convertible body with the blazer’s hood height. But the original registration remained valid. Stock blazer windshield and front glass. Underneath you had whatever blazer you started with good or bad. An excuse to do the 350 v8 swap at the same time.