What defines Gam is the fact he is based in Mamoru, so I don't find any possibility of Emilly being Gam since he was just used as a desguise which ironise the fact Gam was based in Mamoru's physical appearance in all the versions of Magma Taishi.
Note: The antennae are hidding Rino's true ears.
The original Gam from Manga had the antennae replacing his ears.
In the OVA, Gam could change between human ears and antennae at his will.
I can't agree with what you pointed since Emily reminds more of Chocola than Gam or Mamoru.
Here is Milly and Emily:
It's funny how the name of both sounds alike and I would not be surprised if Chocola was playing the character, both also are involved with Atom (Adam in Marine Express) and needed his help.
What is the name of that gangster bellow (he reminds of a gorilla)?
I have seem him in Black Jack too, it would be funny if he was Goa's human version.
He antagonizes the Robot Circus and Rino in the 2003 manga:
By the way, Jeffbert:
The information about Magma befriending Atsushi Murakami is incorrect (http://tezukainenglish.com/bm/character ... agma.shtml), he befriends Mamoru Murakami after he denied giving the camera which had photos of Goa in both manga and tokusatsu versions.
Magma has took the camera by force, but could not prevent from Mamoru tagging along with him since the boy wanted to get the camera back at any cost.
Both arrived in Earth (the planet's guardian himself)'s hideout where the photos of Goa were put in display and Atsushi's camera was given back to Mamoru.
Earth warned Mamoru that humanity had to join forces if they wanted to beat Goa's invasion and Magma took a liking of the boy that he requested Earth to make a son based in the boy.
So, Gam is then born based in Mamoru's image.
Mamoru also got a whistle which would call any of the rocketonians:
One for Gam, two for Mol (actually he NEVER called her in both Manga and tokusatsu) and three for Magma (mainly called when Gam could not hold though enemies).
In the manga, Gam managed to trick Tomoko's impersonator (Mamoru's mother) into believing he was Mamoru and destroyed her after she showed her true form and tried to escape with stolen documents written by Atsushi.
In the tokusatsu, Gam was shorter and younger than Mamoru despite being based off his image, guess it was not easy to find an actor with similar traits of the boy who played Mamoru.
He still wore the same clothes which Mamoru had when he visited Earth's hideout in both manga and tokusatsu.
In the OVA, Gam was never presented to Mamoru when he was sent to Earth's realm, he appeared suddenly posing as Mamoru after he was knocked unconscious after defeating an alien which was posing as a dog.
Gam while posing as Mamoru was kidnapped by Goa who attempted to read his mind, but could not for his shock and then Earth appeared saying that Gam was a decoy.
Later, an alien played by no one other than Skunk attempted to force Mamoru to tell where was Earth's realm, but Gam appeared in time killing the alien and saving both Mamoru and Sayaka (played by Sapphire).
Gam revealed that he was created to be Mamoru's double.
When Goa's lackeys attempted to frame Magma of being the real "devil", Mamoru did his best to prevent Magma from fighting the air force and almost fell for his death when one of the airforce missiles missed the target and had hit the building which Mamoru was standing.
Magma saved Mamoru in time and transported himself and Mamoru to Earth's realm where Mamoru got the whistle which would be used to summon Gam or Magma.
Gam's design in the OVA is pretty much a rocketonian version of Mamoru, but he wear a body armor which is blue and white.
But, he can assume Mamoru's appearance as seem when he fooled Goa into believing he had captured Mamoru.
In note, Rino's desguise is a updated version of Gam's appearance from the manga, but he got more robotic in design since the idea was to make people think that Rino was actually a robot.
While in the manga, Gam wore human like clothes, Rino's desguise had an armor to enforce the idea which he was robot.
Interesting notes about Reno's robot desguise:
a) The antennae (traits of rocketonians) hide Rino's ears.
b) The hair style is similar to Rino without his costume, but painted blue (Gam had a single "spike" of hair, unlike Mamoru, but it's like the difference between the real Atom and Mini-Atom from Count Bat in Tetsuwan Atom original manga and Micro Machines in Tetsuwan Atom 2003 series).
c) Rino's desguise also features a modified version of Gam's face mark from the OVA.
d) Rino's desguise also features a armor just like Gam had in the OVA (though it's diferent) instead of plain clothes.