My major "observation" with all my association with FAST is that even where you are allowed to run an aftermarket block (Hemi's and BB Chevies are allowed due in large part to scarcity) in my opinion you should still be limited to a maximum of .060" over the FACTORY Bore size. IMO it's an unfair advantage to be allowed a 4.56" bore for the Hemi/L87-L89 cars if only because a guy with a small block anything or a Pontiac or any other brand can't. Bigger bores mean bigger valves and the 'already fast' combos get that much faster.
I don't know for sure but I believe the Duster is running an R block so 4.100" + would be no problem. The R block is heavier than a factory block too so there's a weight penalty.
