I recently completely rebuilt a Motorola (Galvin) 55x15 radio. The chassis is labeled HS-9C or HS-90 (the last digit is hard to discern).

Unfortunately, there appears to be zero information available on this particular model. I've been using the schematics for the 55x12 with some success, but the alignment procedure for the RF section lists only two trimmer caps when there are physically three on the dual gang tuner capacitor.

If someone can direct me to any information on the alignment procedure for this radio, it would be most appreciated. Thanks!

Try the 67X12 Motorola. It does have the 3 trimmers with a 2 gang tuner. The alignment should be the same.