Sherman Configuration M4A2 & M4A4

Confused as to which bit goes on which Sherman variant for your M4A2 and M4A4 Shermans in NWE? I am.

From reading this is what I have gleaned.

M4A2
M34 Gun Mount (Narrow Mantlet)
M34A1 Gun Mount (Wide Mantlet)

Choice of either

• 3 Piece Differential Housing
• 1 Piece Differential Housing

M4A4
M34 Gun Mount (Narrow Mantlet)
M34A1 Gun Mount (Wide Mantlet)
3 Piece Differential Housing - not covered in any narrative. Potential that a later reworked vehicle could have it.  But this would be very late 1944 onwards.