I think the fuel requirement of the 565 is the result of dynamic compression brought on by 4.25 stroke verses the 4.00. I am thinking the corresponding valve timing to go along with stroke, creates more cranking pressure than the 540. (did you follow that grads?)

You can bet your ass there is a matching cam change and possibly a intake throttle body change on the 540 to along with the exhaust manifold change from the 520.

Its just what you see at work here.