Is this correct for swapping Master Cylinder from single to dual?

If the pushrod is not anchored in the M/C socket, then I would not use that external return spring, cuz IMO that's just asking for trouble;
Unless your pedal is so darn heavy that the internal one can't keep it up.
But then I would make darn sure the pushrod cannot come out of the socket.
As to the silicon fluid, it still has to be pure to be effective. I use it too.

Hang on, I see that there may not be any way for the pushrod to jump out of the socket if the spring-hat was properly screwed to the back of the M/C. If that's right, then it should all work correctly, once screwed together, so long as the C-ports are open when the pedal is parked.
I may have been a lil hasty, sorry.
That just leaves the rising pedal, which is not normal. Especially not with disc brakes. Generally, on casual stops,the nearer the car is to becoming stopped, the more pedal has to be applied, until just before the final foot or inches. This is just the opposite of drum brakes which are self-energizing.
For the pedal to force it's way back up, under your foot, I see only two scenarios; 1) the piston is being forced back into the caliper; and I see no mechanical way for that to take place,or 2) the brakefluid is expanding.
Ok there is a third possibility; if the rotor is so thin it can't get rid of the heat and it is physically expanding between the pads. But your front rotors should be ventilated .....right...which would preclude that.
That's all I got.