[Mondial]

I would certainly give the Utah transformer a try. If it is rated at 12 Watts and the same physical size as the original it should be fine. Plate current rating should not be of too much concern as it is a push pull output stage and there is not a problem with core saturation since the two plate currents cancel the static magnetic field in the core.

You can also measure the winding DC resistance of the Utah and see how it compares with the original if you are worried about the DC drop due to the winding resistance. You can calculate the impedance transformation by measuring the turns ratio from primary to secondary.