Had a publication arrive this week "Sherman Firefly . Osprey Publishing by David Fletcher , a small book but full on good photo;s and facts no less.
Whilst I will be fully commited to converting the M4A3 to an M4A4 FireFly ,involving Turret ,front and rear Hull modifications ,( + zillion's of other things ! )
it seems that it may be possible to retain the M4A3 late hull and combine it with the FireFly turret , let me explain :-
within its pages it state " At some point undated in 1945 , two M4A3's were taken from US army stocks at Tidworth Salisbury plain and
converted to mount a 17 pounder gun. Whether this can be regarded as prototypes for Amercan FireFly's in not clear ". On March 9th 1945 ,
22 Shermans arrived at Southampton and were met by 26 Transporters . These were duly conveyed to Woolwich London for conversion .
On 11th March 1945 a requirement was specified for 160 FireFly's , later this was dropped to 80 on April 8th. A document later dated 26 May 1945
stated that 86 tanks a mixture of M4 and M4A3 were by this time "in theatre". The recommendation due to shortage of ammunition
( in American service) was to continue the issue to occupation troops or "offered elsewhere" ( what ever that means ).
So it seems ( And please I am not a historian or writing history !, merely presenting the details recorded in a printed publication ) it may
be an option for some to convert the turret to FireFly specification and place it on the hull of a late M4A3 and still have a correct version of a
Sherman FireFly ( US Issue ) abiet at a very late war period . Now dont shoot the messenger ! .lol

Yesterday is our history, Tomorrow is an eternal mistery, Today is a gift, its why its called "The Present".