For the correct designations for US Tanks of WW2, you can't do better than Hanno's web site, which I have just spotted on one of the other threads:-
British designations for US medium tanks and related AFVs
According to the above, the welded hull M3A3 was also supplied to the British as the Grant II, so thats confirmed it for me - the Grant ACV in Tuscany is a welded hull Grant II and the Division had two separate vehicles. See attached photo for the other one in Bologna April 1945.
So we now know the Grant in Tuscany didn't have to have its hull taken from a 'left over' US Army Lee and be combined with a spare Grant turret, as it was built as a M3A3 / Grant II. Only later was it modified to an ACV, most probably in Egypt, where the 6th SA Div assembled prior to going to Italy.