Pick a pin height your happy to use
Work back to the lightest bobwieght you can with a chev journal rod on either stroke

Aside from the intake, does it have to be a rb block?
In a 400 block a 537 gram Diamond 1.32 piston, one of their custom 130g pins and a 712g k1 6.535 2.1 rod on a 4.25 crank will get you a target bobwieght of around 1870 grams - it would take some exotic components to get a rb down to that, at that stroke