Just got a third party mounting ring.
I tested the whole setup again, and the balance issue is completely fixed. Balance point is the same for both side of the meridian now.
The setup consists of a Gitzo G106 tripod, a Takahashi TG-SP II mount. I'm still using the good old Intes dovetail mounting plate since the new one from ScopeStuff has mounting holes which is recessed too deep for the mounting screw head to a degree such that the mounting screw cannot sit all the way inside the socket. In short, I need to buy shorter (around 1cm) 1/4" screws in order to use this new and longer dovetail. A Borg 45ED II is mounted by the socket on the tube rather than the focuser to reach good balance. A Canon 450D with a 200mm f2.8L is used, and they're mounted by that mounting ring.
There's no place for the Konica Minolta Z5 for video taking for that old dovetail since it's too short. I tried to put a ball head on the counter weight side of the setup, but I have no suitable screw for that purpose. The screw head is too small for that hole.