TY for the responses, everyone. TY for the link Wobbly - but my bike is a K2 using carbs with the casting #7a. Do have another (used) float bowl to try but unfortunately it was a victim of too much simple green, and is now a dark shade of german panzer grey.
Haven't narrowed down exactly where the crack is, but have installed new float valves, set new floats, and double checked them with a clear tube test...everything passes except the #2 carb wants to drip from the overflow tube. Think I'll try the brass tube idea next.