[SCOBRAC]

Nothing wrong with a an industrial engine provided all the cylinders line up, some didn't.

I'm not sure why your aluminum heads aren't working well for you enless the chamber size has changed, that said the principal advantage in aluminum anything is weight reduction. You cut almost 100 pounds off the weight of the engine using aluminum. Of course they are easier to port and tend to be less likely to have hot spots, which in a small way allows for increased compression. Hot Rod Magazine did an interesting article recently comparing aluminum to cast iron. The results were interesting, they concluded that comparing apples to apples and all things being the same weight was the only advantage to aluminum. That said good 428 heads and 427 lowrise heads are getting hard to find, so aluminum might make sense financially as well.

How much of a notch do you need for a 427 MR (2.19" intake valve) to fit? The 427's notched the cylinder. Assuming something around 4.13" bore V. the 4.23" 427 bore that's a lot of notching. It depends on what kind of lift you want, but I think for a street motor the point of diminishing return might be at 2.09" valves. That said I run tunnel port valves in my 427 and really enjoy the flexability it provides. I'm not sure I'm aware of anyone doing it with a 428. It wouldn't be cheap. I have about $3,000 in additional head / intake work to make the Tunnel Port configuration make sense. Valve size is only 1/2 the equation. The theory obviously is to stuff as much mixture into a cylinder and light the fuse. Potential intake volume / flow is wonderful, but only useful when the potential is maximized. This is only into the case of a 2.19" and 2.25" intake valve when compression matches the increased capacity. You really want to run that kind of compression?

The difference between a standard 428 CJ head and a 427 Medium Rise head configuration in terms of flow potential is about 50 cubic feet of air a minute. The potential horsepower increase is about 100 assuming a .600" lift. Of course this assumes you want and are willing to live with a 500+ HP FE in your car. You may simply not want or need that much excitement in your life, nor the increased costs associated with it.

The maximum power potential of any engine is limited, ultimately, by how much power-producing air/fuel mixture can be processed by the four cycles of the engine: Intake, Compression, Power, and Exhaust. Perhaps the single most critical piece of data in this very complex calculation is the amount of air/fuel mixture that can be passed through the intake port.

Increasing an engine’s displacement will enable it to produce a given level of power at a lower RPM, but ultimately, it is the flow capacity of the intake tract that will limit peak power, regardless of the swept volume of the cylinders.

I think you have a solid plan. Best of luck.