Mike, I would not run the dual port Offy. I have had a few freinds complain about the dual port. But the regular 4bbl. intakes were well liked.
I see absoultey no reason why it can not be done and done well without killing mileage or throttle response in any way shape or form. You'll just need to do one thing.....
Take your time and tune it well.
I think a 500 CFM would do fine. 600 is doable. Take a look at the bore of the 2bbl. Your 4bbl. primary should not be larger. Or, at most, barley.
