Bill, I'm really not into the design history of the slant, but (this is my opinion), I disagree with the statement (I have heard this before) that the slant six was designed as an aluminum engine, and therefore the cast iron version is much stronger. I have looked at both blocks.
If you compare the aluminum block to the cast Iron block, there are many differences. The aluminum block has main saddles that are iron/steel and bolt into the block. The deck on a aluminum engine is open (you can look down right into the water jacket), and has free standing cylinders. The side of the block is a different configuation. I would submit that if the cast iron block had been cast the same as the aluminum block, the current cast iron block would be stronger.
PS: I do believe in turbos on a slant. Go for it.
