If you want the sound of old Byrds stuff with a RIC12, then you should get a Fender tube amp. Something like a Twin Reverb, Super Reverb, Showman, Bassman, etc would be fine. Get what you need for the volume you need, and any of the Blackface stuff should work fine. Silverface stuff will be ok too but not as good. Modern Fender will get you in the ballpark but again the BF tone is where it is at when trying to nail old Byrds stuff. Tweed Fender tone isn't quite right for it but it will work. You can get somewhat close with the Vox sounds, though those are more suited for nailing Beatles 12 string tones. A good compressor is a requirement too.