Glory of Christ is the Glory of the Father as well, for this Glory pertains to both eternally, that is to say, also before the world was created (John 17:15), for time started only together with the world, being its measure, but before the world was created there is atemporality of God's glorious eternal being, which being is likewise proper both to the Father and the Son, who is the "Image and Radiance of God's Glory" (Hebrews 1:3). As the rays of the sun's glowing disc can be regarded as "image of the glowing of the sun", with an implication that the glowing disc cannot not emit its image - the rays/the radiance, to the effect that the radiance is the necessary consequence of the glowing of the disc of the sun, similarly, the Logos is the Image of the Father's Glory, to the effect that this Glory cannot but be expressed and entirely present in the Logos, with the consequence that the Logos is as necessary as the Father Himself from whom He is born, analogously as the radiance is necessarily "born" from the glowing disc of the sun.
Therefore, in the Pauline expression, the "Gospel of the Glory of Christ" indicates the divinity of Christ, for this is the eternal Glory of the Father and His co-eternal Logos, who in Jesus Christ is presented already as the Incarnate God.
Now, does it differ from Mark's expression "Kingdom of God is at hand"? In a very general sense, no, it is the same, for Kingdom of God is a name of God's - eternal King's - loving and intimate presence among His creatures, whom He grants this most intimate communication with Him through His Son. But this also means that in the Kingdom the Father and the Son communicate to the creatures that very Glory that They have even before the creatures were created by Them, the eternal divine Glory; indeed, Jesus does not grudge His and His Father's eternal Glory from humans, but even enjoins them to pursue it (John 12:23). But even without relationship with the creatures the Glory of the Father and the Son remains as it is, eternally, the "Kingdom" is a token word standing for communication of this Glory to creatures through the Incarnation of the Logos.