[Arran]

Generally speaking it's the primary to secondary ratio that's more important then the primary impedance, that's why those universal output type transformers have multiple taps on the secondary side but not the primary side. The #42 has the same plate impedance as a 6F6 and is fairly close to a 6V6/6BQ5, and close enough to a 6L6, so a salvaged transformer for any of these will work fairly well. What will not work well is an output transformer intended for a type #41, 6K6, or a 6AQ5, those are way off the beam. The only wild card is the weird voice coil impedance of some Philco speakers, most are either 4 or 8 Ohms impedance not 1.1 Ohms, that is if the 1.1 Ohms is an impedance and not a DC resistance.
Regards
Arran