Too brittle, maybe yes, maybe no.
The photos of frame LOOK like it is malleable(hopefully) cast iron. Hopkins & Allen malleable iron frames were commonly used on pepperbox guns. As the frame in a pepperbox is not under stress from the powder explosion that's not too bad, being in a pepperbox. In a revolver the frame does hold the thing together when fired.
Please bear in mind that in the 19th century there was no way to know if that malleable iron was indeed "malleable" It all depended on how accurate was the chemistry of the casting, and was it heat treated right (about 1750F 24 hours)
Your P.I.T.A. metallurgist. Again.