All steel... Nice.
I wonder just what rod ratio you could get with custom pistons on a 4" stroke.
I know 6.385 rods will work with a 4.25 stroke, so with that same piston, you could fit a 6.51 rod.
6.535 is an available size that could almost certainly work but that would only give you a ratio of 1.634 with a 4" stroke.
To get to 1.7 you'd need a 6.80 rod. I kinda doubt that would fit, so you're probably right about not being able to go with a 4" stroke.
I know there's some advantages to a long rod setup but it's not like 1.634 is a bad ratio. It sure would be nice to take advantage of the 4" aftermarket cranks out there rather than having to modify an old 396/427 crank.
Either way, it should be a great engine with a blower on it.