Why is that a concern, exactly? I thought the issue was the fact that the NDS cup wasn't threaded in as much as usual, which the spindle being made for a 70mm bottom bracket would explain.

The space you'll have between the NDS crank arm and the cup looks perfectly normal to me but you haven't shown what it looks like with the crank arm on so that's only a hunch. In my experience after the crank arm is pressed on there's typically only 2-3mm between the cup and arm. Obviously a lot more space is required on the drive side but unless if you have super flared chain stays it shouldn't be an issue on the NDS.