Hi Peter,
Mixed vehickles were more common than you might think. British and Commmonwealth units often had a mix of tanks divided by Sqns so you might get Crusaders in A Sqn, Grants in B Sqn and Shermans in C Sqn.
I read a few unit war diaries a while ago when I started looking into the M4A1 Mk II and the M4A2 Sherman III. It was not unusual for units to have what they termed light tanks and heavy tanks, Crusaders and Shermans or Crusaders and Grants well into 43 and after. Replacement Crusaders and Sherman were arriving in equal numbers in some units well in to mid August 43 which is as far as I went. Tanks were taken over from the Americans and so on.
After the invasion of Italy the main focus was on the build up for the invasions of Europe so they got the pick of the crop so to speak.
So Italy has lots of possibilities for mixed armour.
Cheers
Al