I don't know the direct answers to you questions, but have a few comments to consider...

I do not consider 225 to be an overheat situation. It's fairly normal in my opinion, but admit it's getting to the upper limits of comfort if it stays there often. But if it never exceeds that number you might be fine. Factory recommended 190 t-stat in these cars.

As for you doing "the usual"...

1. Cast impeller pumps are generally considered to be better at moving coolant than stamped.

2. Electric fan/shroud have been shown time and again to not cool nearly as well as a factory belt driven fan/shroud setup on these Firebirds.

3. According to Flex-A-Lite, 2000 CFM is not enough for a V8...they recommend 2500 for minimum:
http://flex-a-lite-blog.com/2010/04/24/how-to-choose-an-electric-fan/

You don't mention shrouding in front of the radiator. Do you have proper x-panels in place at front of radiator support? Lower baffles? Side baffles? Need everything in place to direct air thru the radiator and not around it, and the electric fan & shroud with small diameter openings they have in comparison to factory shroud makes this more challenging and more critical.