That sounds like an E. N. Santa Barbara.
I have a few, they have a good reputation and I like them.
I don't have any conversion cylinders for any of them.
If you get a hold of a conversion cylinder manufacturer like Taylor's for example, I expect they can give you a better answer. (they might ask you for some dimensions, or to send it in)
Those revolvers haven't been made in quite a while and I'd expect a wider range of tolerances with more hand fitting than a recent CNC machined revolver.