Granted, the fwd 300M (not the concept car by the same name) was not fully regarded as "A Letter Car" by many. Then one showed up at the 300 Letter Car national even at an Air Force Base in Nevada, with very loonngg runways. Naturally, there was some drag racing and such. The Chrysler operative was there with a 300M, for comparison.
Many of the Letter Car operatives, who scoffed at the fwd car's credentials, were taken for rides down the quarter mile and to top speed. In almost every measure of performance, the 300M bested the earlier cars. Now, it was reported that the vintage letter cars might not have been in their best "road test" tune, reflected in their 1/4 mile times, but even by earlier magazine road tests, the 300M left them in its dust, so to speak. All the way to a top speed of about 140mph, stock.
It also seems that a lead engineer on that project, bought a 300F (or 300E?) and drove it back from CA to MI, so he could get a full measure of what the cars were about. Neat move, I thought at the time!
End result, the Letter Car owners came to respect the 300M in a very positive manner. I rented a good number of 300Ms from Dollar car rental (as they were a unit of Chrysler at the time) and liked them a lot. But I liked the original LH cars a lot, too.
The "M" might not be as "rough and tumble brash" as the original Letter Cars might have been, being a bit more refined in nature, but they certainly perform better, as a modern alternative. But by the time of the 300-L, a lot of the brashness had diminished, leaving a "luxury car which performs" as a result. In THAT orientation, the newer 300M can fit right in.
Enjoy!
CBODY67