You can easily google "75mm Howitzer Motor Carriage M8" and get a plethora of information regarding them. Some of it is even correct. If he was a "gunner of 75mm" and he was in the HQ&HQ Company of and Armored Infantry Battalion, then he was gunner on an 75mm Howitzer Motor Carriage M8. Three of those, along with two armored Half-tracks M3A1, and one Jeep, comprised the Assault Gun Platoon of the Armored Infantry Battalion's HQ&HQ Company. It was comprised of 1 officer and 23 enlisted men. Twelve of the enlisted men made up the crews of the three M8, a commander, driver, gunner, and assistant driver each, while the rest rode in the jeep and half-tracks. The Armored Infantry Battalion, HQ&HQ Company also had a Reconnaissance Platoon. It was comprised of one officer and 20 enlisted men one Half-track M3A1 and four Jeeps. It had no Scout Cars M20 or Armored Cars M8 ("Greyhound" was a nickname given to them by the British and was almost never used by U.S. Army personnel during the war). Thus, he was unlikely to have been a crewman in either of those vehicles.
thank you for the information now i have many hours of internet searching and reading to do......thank you ted