A lot of things are proposed here. I'll keep it short: I agree with FLCL with everything he said about those Pokémon, though I see Metang even as a candidate for A-rank now Emboar and Absol are gone and Musharna rises in usage.
Zangoose down to A-rank: Agreed completely. No need to repeat Constantinipple, though it is worth noting that Regirock should not use Stone Edge, but Drain Punch against Zangoose for several reasons (same damage output due to Zangoose's fighting weakness, but 100% accuracy and recovery).
Also, teams with Regirock or Metang don't even need to sac something against Zangoose. They can just switch in.
I agree with SweetJesus about Vigoroth for C-rank and Tangela for A-rank respectively.
Torterra for A-rank... hm. Questionable, since it needs three attacks (STAB + Stone Edge) if it does not want to be walled. Without Woodhammer, opposing Torterra wall it, without Earthquake, Steels wall it, without Stone Edge, any double-type consisting of Bug/Grass/Flying walls it. It has a lot of support options, but these don't matter if Leavanny or Butterfree comes in for the kill. They will win even if Torterra has finished setting up Dual Screens. I suggest Torterra stays where it is. I'd say it is fine in B-rank.