I saw that sale, too and am tempted, but...naw, no need for yet another "project" at this time!
They also have this replacement frame on sale:
Brooks Saddle Backplate Braket Assembly Chrome 8 x 6.25 | Parts & Accessories | Saddles | All Products | Bikewagon
they don't say what model if would fit, but if the measurements are accurate it's a very short frame, for some "S" or Lady's saddle, possibly a "Junior".
Rudi Mayr might know...
And there's a cantle-only for the B-66, just one left in-stock:
Brooks Saddle B-66 Backplate with Bolts 7.5" Black | Parts & Accessories | Saddles | All Products | Bikewagon