I have a BoB Sherman kit and I want to use the oval loaders hatch turret. What changes need to be made to the hull to allow the oval hatch and possibly the muzzle brake to be used?

I assume BoB means Battle of the Bulge, not Band of Brothers...

To my knowledge no changes are needed on the hull to use the later turret. Be sure to use late raised return roller bogies (but I think you should use these in any case on a 76mm M4A3 VVSS). If you want to make a very late version you might have to add the later exhaust deflector and rear view mirrors, but I'd check references first. In any case, hulls and turrets of knocked out tanks were combined all the time, so theoretically any combination of earlier and later components would be possible (according to Belton Cooper's "Death Traps").

Someone will probably come up with a better answer soon...

Cheers
Stef

As far as I know, no mods to the Hull are necessary. You might want toi go with track with the duckbills on them, they are very common on late war Shermans. If yiu get the later release (without the tank crew) I think that it comes with Duck Bill track

Hull design was basically unchanged. There were very minor changes over time, notably to the top edge of the glacis plate, which had small areas ground away to provide a wider field of view for the periscopes. The width of these ground areas varied, but it's hard to spot, and usually invisible in combat photos. I don't know if the BoB kit still had the recessed weld joints on the hull top--if so, add some filler so the welds are above the surrounding plates, not below.
Dragon has reissued this kit as the Premium Edition M4A3, with numerous small improvements, including a corrected upper turret shell for the oval hatch version. They slightly changed the angle of the hatch opening, and made the casting around the pistol port a little more prominent. The kit also includes the earlier dual cupola version. This turret sprue is also included in the "Thunderbolt VII" HVSS version.