You could have got away with it if it wasn't for those meddling kids and that pesky dog!
Sorry, couldn't resist.
It's also my understanding that the Firefly conversions were only undertaken on Sherman M4s, M4 Composites and M4A4s, with the vast majority M4A4s. Didn't they also have two top hatches to facilitate gunner evacuation? Not that it matters too much, you might as well get use out of them. As Tanktastic said they're for wargaming and a bit of dressing will sort them out!