Sean,
Its a great old kit, typical of Tamiya quality but also a couple of typical tamiya oversights (eg. no lenses in cupola)
backdating to a mark 2 is a massive undertaking in itself. Let alone the massive task of doing the bridge, i'd think carefully about that before going fo it as it really is a big job. You'd also probably be better off using AFV clubs upcoming Churchill Mk.III kit. That would save you having to replace the hull front, scratch build square hatches, add all the side rivet detail, re-build the mud chutes etc. etc. though you'd still have to replace the air intakes with the earlier variants.
Still scratching an early cast turret would be a big job too, but hopefully AFV club will follow up with a variety of early variants using their Mk. III as a base, kind of as they did with their Centurion line.
The toad is a real mean looking AFV, I saw some pics of the restored one at the war and peace show. Would make for a nice kit.
As for the turret, they do have some play when fitted, you could perhaps fix that with a shim if it bothers you, although it won't really matter when the kit is finished. I've checked both my kits and the turrets both fit on fine, perhaps check the fit of your two turret halves, or perhaps the ring underneath has some excess material on it?
Good luck, and post some pics up as i'd love to see your build.
James