I've read some people talking about how many frags you get per Ginkaku dupe

All Edo Rares/Super Rare dupes get you 25 frags, while in GNW you get 10, like any other 2*

Edo Treasure's already got halved rates anyways, with around 30 per rare and 120 per super.

But the best way to get skillbroken Ginkaku would probably be piecing him together from events or GNW, Edo Treasure's not worth too much right now, unless you want a 3* Super, or faster 4* Mu or something.