[RodB]

Hello Bill and welcome to the Phorum. You are definitely a brave person to attack a vintage auto radio. Who knows what that radio went through. Before you can look at sensitivity consider the antenna. The auto antenna must be tuned to peak for optimum performance therfore, the actual antenna from the vehicle, or similar coat hanger, should be used. There's probably a trimmer cap in the antenna circuit.
The buzz is probably coming from the power supply vibrator. Be sure all the capacitors in the vibrator circuit are replaced. You may have to clean vibrator contacts. When you get to the alignment do the IF first. That should improve sensitivity and selectivity. To bring the tracking to where it should be adjust the oscillator trimmer capacitors/coil cores. I'm being general with my comments because I don't have a schematic. I'm sure others will have more specific comments. GL