using carbs from a smaller engine (lower CFM rating) is also typically recommended. But you are fitting to a 207 so I am not sure that there are any Carter OEM carbs out there from a smaller engine.
Not sure if Carter W1 or WA1 were fitted to a smaller engine then a Nash 184. But you could use a pair of Carter W-O carbs. The Model 513s was fitted to the Nash 172. The Model 507s was fitted to the little Wllys 134 (4 cylinder).
