Sherman Firefly V C would be for the Brits, not US and due to the penetration on the 17lber would need to be perked somewhat, lest Tiger Is cease to be really viable.
The Wirbelwind would be fine. If it was too viscious it could always be lightly perked later, like the F4U-1C.
I'm not sure the 88 would be needed along with the Wirbelwind and Ostwind.
A M4A3 Sherman with either the 75mm or 76mm gun would be a great addition too.