On the opus 68: The original was for rather a modester choir; the opus 68b has expanded writing for a proper choir. If you engage instrumentalists, I think the piece could be made to accommodate any grouping.
On the opus 52: Possibly textually unsuited to FCB, though this is an original setting of a text which I found that Gustav Holst had set.
The unaccompanied Introit I send just for your own bemusement; utterly unsuited to FCB.
I may have another potential candidate to hand, if so will send separately.