Woops
how to look like a fool, it's not a whole new turret you need just gun/mantlet/hatch
Have a look at Terry's review of the german KV and the corresponding russian original may help
http://www.perthmilitarymodelling.com/reviews/vehicles/trumpeter/tr00366.htmDepending on what's in your kit you could pinch one of the rear hatches (cover the hole in canvas sheet/stowage) to use on the turret as they're visualy similar
(actually I think the turret hatch should be slightly larger than the rear ones, but Trumpeter's kits have them the same size)
good luck