Geoff;
Heres two more references I found:
From Zuehlke's The Liri Valley: "
The company's White scout cars"
and from Dancocks' The D-Day Dodgers: "
Rolling up to the Melfa in their White scout cars (this was one of the few occasions in Italy that this motorized infantry unit was able to take these American-built armoured vehicles into action)"
Judging by what I've read this morning, I would say that Maj Mahony's coy was mounted on White Scout Cars going into the Melfa action.
Cheers