"Here is my guess:  Mansfield, LA, March 8-9, 1958.  Jim Hall drove a 250S #69 to a win in race 4, but started race 7, the feature, with another 250S [race number unknown, but #68 is close to his other car]. In the feature he finished 3rd behind Frank Davis and Ebb Rose [who drove a 300S but normally used #44]."

"At Galveston in April 1958 Jim Hall raced one of his 250S Masers with #68 as well. However, there the shape of the race numbers was different and the photos are clearly not Galveston."

From German Maserati expert Walter Bäumer:

"Yes, this could also be the case!  It's then a 250S as the driver is quite tall in this smaller car than a 300S!   If so, its then either chassis #2431 or #2432!  Mit besten Grüssen / Best wishes!"