Here's the thing
"Following a massive decline in orders for tracked combat vehicles between 1983 and 1994 FMC and the Harsco Corporation agreed in January 1994 to combine their defense businesses to form United Defense. The new company owned the former FMC California-based Ground Systems Division and Harsco's Pennsylvania-based BMY Combat Systems Division. The new company restructured its operations to concentrate final assembly and testing to Pennsylvania."
https://en.wikipedia.org/wiki/United_Defense
M8 Armored Gun System was a light tank that was intended to replace the
M551 Sheridan in the 82nd Airborne Division, as well as being expected to replace TOW-equipped Humvees in the 2d Armored Cavalry Regiment (2nd ACR). It was to enter production in 1996, this never happened. This might entered service in the Twilight War as replacement for the US M551 Sheridan and the US ACR's TOW-equipped Humvees and possible a replacment for the M41 Walker Bulldog and M24 Chaffee still in service with some NATO nations.
https://en.wikipedia.org/wiki/M8_Armored_Gun_System
By contrast the Stingray is already in production and in service (Thailand) by the start of the Twlight war. This might make more appleaing since is a proven? design and in production. I could see the AGS-Sheridan coming online later in the Twilight War.
The AGS-Sheridan was a mating of the standard M551 Sheridan hull with the turret of the Stingray light tank.
http://en.wikipedia.org/wiki/Stingray_light_tank