Yes my NGV is also very tight on the tunnel.
I agree with you that the accuracy of the outer case is a important factor when engine assembly. The rear plane of it positions the bore axis of the NGV which shall be line with the shaft. Unfortunately the structure of sheet brings a little error can destroy the concentricity. So I think this is the reason why the gap between turbine blade and NGV is different. Is it true that KJ66 has two thick flanges can ensure a fine plane?

To fit the eight screws in the holes of the case is not very difficult. Also the enlarged holes on the side wall of the case normally can align with the holes on the diffuser.

I replace a new turbine wheel last night and wait to run. Hope it has no vibration problem.