I want to get two new texas heat speakers and i dont know what ohm rating would be correct. Since the cab is 16 ohm's im assuming the sheffields in it would be 16 ohms too right?
Could be all 4 ohms in series, or 16 ohms in in parallel/series configuration.
I'd put my money on all of the speakers being 16 ohm, to be quite honest. You can always disconnect one and test it with a multimeter to get an approximation - you will only get resistance rather than impedance, but the difference should be big enough that you can assume what impedance the speaker is.