1966 Plymouth Valiant Signet Hardtop

2legit2quit, you don't need to change out your K frame or change your drop link if you stay with stock front suspension, if you go this way you should look at new motor mounts if they are original. Sub frame connectors are also a good add on.
If you want to run coil overs you can look at HemiDenny Hemmy Denny or Reilly MotorSports, Inc. but these are not cheap but both make suspension coil overs for early Abodies.