@ The Reptile: If I understand correctly, Blissey would have 75 special because its special defense isn't its highest stat (HP is), so you use the lower of the two.
But Chansey has 105 Spc in RBY. If I follow your logic, RBY Blissey would have:
HP: 255
Atk: 10
Def: 10
Spc: 75 (down from 135 because its HP is its highest stat)
Spe: 55
Now compare to RBY Chansey:
HP: 250
Atk: 5
Def: 5
Spc: 105
Spe: 50
It sounds like nonsense to give its evolved form a lower Spc. Evolved forms should follow the same Special trend than their pre-evolutions if the latter were in RBY.
On-topic, let's see if Tangrowth can have some usage here...
Tangrowth
HP: 100
Atk: 100
Def: 125
Spc: 110 (because Tangela had 100 Spc in RBY and ended with 100/40 in later gens)
Spe: 50
With much better Attack and HP stats than Tangela, Tangrowth can now go mixed.
-Swords Dance
-Bind
-Mega Drain
-Stun Spore / Sleep Powder / Hyper Beam
RBY Tangrowth is quite hard to destroy with these insane defensive stats. Swords Dance + Bind will remove a lot of health from its opponents. Mega Drain is for recovery and STAB. Stun Spore and Sleep Powder will ease your sweeping (read: annoying) prowess. But if you feel lucky, you can try Hyper Beam when your opponent is low on health.