I'm not convinced it's that simple.
Power = thrust x TAS.
Therefore Thrust = Power / TAS
Therefore Thrust = Power / (CAS / SQRT(relative density))
The power curve will vary with airspeed and density, so the relationship will be a fairly complex one. I wouldn't be surprised if best thrust is achieved below max RPM under certain circumstances, since in many aircraft types max RPM means some local supersonic flow at the tips and an associated loss of propeller efficiency.
Also VMCA is not defined by climb rate, it is the minimum speed at which a given level of control can be obtained - no more than 20° heading change following sudden failure of the critical engine, no more than 5° bank when trimmed for straight flight subsequently, the ability to roll at-least 20° each way, and yaw 15° both ways with no more than 150lbf foot-force.
The SEI / MEI best climb speed is a separate concept to VMCA but obviously will be no lower than VMCA (which itself incidentally isn't allowed to be less than 1.2Vs).
G