For this method, in a V8 with 90° bank angle, the relationship: balance weight = 100% of rotating mass + 50% of reciprocating mass. Other engines vary all over the map.

Not that easy.
A connecting rod has, by popular convention, its weight divided into reciprocating (top) and rotating (bottom) components. The line of division is the center of gravity.
Missing from this equation: a really long rod (3:1 ratio) has most of its reciprocating thrust in the vertical plane, a short rod (1.3:1) has a far larger horizontal component.
Conventional balancing completely ignores this (but it's critical to motorcycle engines).