Generally, if the oscillator does not have a padder (series) trimming capacitor, you can adjust the parallel trimming capacitor to line up the high end, and adjust the IF transformers to line up the low end. It could be that your signal generator is off-frequency. Use stations on the dial for exact alignment, and be sure that the dial pointer stops evenly at each end of the dial. Adjust the high end so that it falls where it should, and then go to the low end. Tune in a station and then tune off of the station slightly up the dial. Adjust the IF transformers until the station again comes in loudly. Adjust a little more up the dial and readjust the IF transformers. Then go back to the high end of the dial and realign a station there with the oscillator trimmer (parallel) capacitor. Go back to the low end and keep moving the stations up the dial. Repeat this until everything falls where it should. This procedure can work quite well. Once finished, touch up the antenna trimmer cap for the high end of the dial.
You can run into trouble, however, when an oscillator padder (series) cap is used, as this also adjusts the low end of the dial. If this and the IF transformers don't sync, you'll have dead spots on the dial. Also, if a tuned RF front end is used, as is often the case, perfect synchronization is necessary, and it is much more difficult to move things around when necessary. However, it can be done.
Also, many car radios use slug tuning. I'd say touch up the slug tuning for the high end of the dial and then use the IF transformers to move the low end.
Without knowing your exact radio, however, I cannot give exact instructions as to how to adjust it. If your signal generator might be off and you have a long wave receiver handy of the accurate digital type, you can compare your signal generator to that, as those radios tune down into the IF territory of most AM radios.
T.