Even though it is historical, I don’t like closing off the Black Sea. Unless you make some corresponding change that helps the Axis, this rule is almost a complete give to the Allies by taking away one of the more relevant uses for the Italian Navy. Maybe a middle ground would be to apply a penalty to entering the strait (loss of IPCs, minefield that rolls on “1” like AA fire, etc) instead of closing it completely.
On the improved IC production, I think this is another change that hurts the Axis (particularly Japan) more than the Allies. Another option might be to limit, but not eliminate, the use of improved factories in low IPC territories. For example, allow factories in territories of 2 IPC value or less to increase production by one but don’t let them have the benefit of lower repair costs.
On a more general note, I think the whole tech structure needs to be re-worked. I like the concept of tech, but under the OOB rules, one lucky tech roll can effectively throw the game (i.e. Heavy Bomber to the U.S. on round 1). No tech should be that powerful. There are a number of different ways the tech rules could be modified, but I think it starts with an acknowledgment that the OOB rules don’t work very well if the object is to keep the game balanced and not dependent on a luck tech roll.