Of the ones I've seen, southern rifles that have them appear to have been retrofitted when converted to percussion, but I don't think it is a horrible stretch to use one on a flintlock, esp. if you posit the period was near the "cusp" of flintlock to percussion transition. I used a heavily modified (esp. in tang area) "Hawken Flint Patent Breech" on a southern style rifle to replicate an original that had one in percussion conversion. It is not a true Nock type, but the one on the left in Dan's picture, with the touchhole going directly into the "main"/smaller diameter chamber.
Functionally, it works beyond my expectations. Ignition is fast and if anything it fouls less than my regular breech flinter. I don't think I drilled out the chamber much if any, but I did cone the top of the chamber and polish it out. I noticed that wiping the bore doesn't cause any trouble with fouling the touch hole. This is important because it is a target rifle that also pulls chunk duty.
Accuracy with the hook is not a problem because I took extra care to make sure it locks up tight, and I added a couple of extra screws, one in the standing breech (from the bottom to pull it down) and one that can push the breech up from the bottom (it doubles as a front TG "screw"). I haven't needed these screws yet, but I know I can tighten up the interface if necessary with them, in a couple of different ways. The screw in the standing breech can be lengthened to lock the hook in (at the expense of easy disassembly) and/or the screw beneath the breech if lengthened will wedge the barrel hook tighter into the socket in the standing breech. Probably overkill and it shortens the space available for a Ramrod, but that is a good tradeoff in my application . I got this idea from a Dan Phariss post about screw in the standing breech and/or from below.
PS. The breech you reference is the same one I used, except mine was the 1 1/8" size.