[Chas]

Eric,
 
I gather that the original Zenith "loop" is not in place, another loop may not have the correct inductance, but that can be fixed.

Look at the RF stage schema, the loop that is tuned is connected to the stator of the tuning condenser, (not the oscillator section) AND the loop returns to the AVC line, that wire may be soldered to the bottom of the tuning condenser frame and schema says "WH-BRN" a wire with a tracer, that is AVC... The tuning condenser frame is insulated from the chassis.

If the cold end of the loop is connected to chassis there will be no control over the RF amp, AVC will work poorly.

But, if your happy...

   

Oh goody, that printed nice and big

If after connecting as shown in schema and the radio works poorly, then the "new" loop will have to have turns added or removed. There is a trick to determine what to do but only if you need to tune that loop...   chas