Has anyone used a modern Sirius chrysler antenna on an old Mopar?

Subscription (Sirius) does not operate on AM/FM frequencies. I know nothing about this antenna. I would guess it would not work well on AM/FM

"The short answer" is remember the old 9 ft CB whips? That was a "quarter wavelength" on CB frequency band. That would be one form of "optimized" antenna. Generally, the shorter the antenna and the lower the frequency, the worse things work. Factory AM FM antennas are a compromise at best in the AM band. On FM "they ain't bad". A quarter wave on the FM band (88-108 mhz) is roughly 2 ft long at 108, about 2 1/2 at 88mhz

A REALLY GOOD AM antenna LOL would require a balloon to keep it aloft!! (425 to 137 feet)